feat(m5): gui shell

- AppServices composition root: owns config, global workspace registry
  (app.db), platform path comparer and the LRU workspace connection pool;
  configuration persisted once at shutdown and services disposed
- AppDataPaths centralizes app.json / app.db locations; AppConfig gains
  a DefaultLanguage constant
- MVVM shell: MainWindowViewModel hosts SidebarViewModel and the current
  content page (welcome / workspace / localized failure state), mapping
  typed open failures to ResX messages
- SidebarViewModel: persistent workspace list with name-asc, name-desc
  and recently-updated sorting (selection persisted), open-project folder
  picker and initialize confirmation via Interaction<TInput,TOutput>
  handlers registered by the view; workspace entries open/remove
- Pages (welcome, workspace, message), dialogs (settings, about, confirm)
  with their view models; settings/about opened from the window
- App startup applies configured culture (RTL flow direction) and theme
  before the main window; forwarded IPC commands activate the window and
  switch workspace from the launch path
- Full UI text sourced from ResX in both en and zh-Hans; no hardcoded
  strings, theme colors via ThemeDictionaries

YKanBan/App.axaml

@@ -1,9 +1,27 @@
 <Application xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              x:Class="YKanBan.App"
+             xmlns:semi="https://irihi.tech/semi"
              RequestedThemeVariant="Default">
 
     <Application.Styles>
-        <FluentTheme />
+        <semi:SemiTheme />
     </Application.Styles>
+
+    <!--Custom colors MUST be declared as Light/Dark pairs inside ThemeDictionaries
+        and consumed via DynamicResource so theme switches restyle everything.-->
+    <Application.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.ThemeDictionaries>
+                <ResourceDictionary x:Key="Light">
+                    <SolidColorBrush x:Key="SidebarBackgroundBrush" Color="#F6F7F9"/>
+                    <SolidColorBrush x:Key="SidebarBorderBrush" Color="#E2E4EA"/>
+                </ResourceDictionary>
+                <ResourceDictionary x:Key="Dark">
+                    <SolidColorBrush x:Key="SidebarBackgroundBrush" Color="#1C1E24"/>
+                    <SolidColorBrush x:Key="SidebarBorderBrush" Color="#2C2F37"/>
+                </ResourceDictionary>
+            </ResourceDictionary.ThemeDictionaries>
+        </ResourceDictionary>
+    </Application.Resources>
 </Application>

YKanBan/App.axaml.cs

@@ -1,18 +1,29 @@
-using System.Linq;
+using System.Globalization;
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Data.Core;
 using Avalonia.Data.Core.Plugins;
 using Avalonia.Markup.Xaml;
+using Avalonia.Media;
+using Avalonia.Styling;
 using Avalonia.Threading;
 using YKanBan.Ipc;
+using YKanBan.Services;
+using YKanBan.Storage.AppData;
 using YKanBan.ViewModels;
 using YKanBan.Views;
+using Resx = YKanBan.Resources;
 
 namespace YKanBan;
 
 public partial class App : Application
 {
+    /// <summary>Composition root, created before the main window.</summary>
+    public static AppServices Services { get; } = new();
+
+    /// <summary>The language applied at startup; a live selection differing from it needs a restart.</summary>
+    public static string StartupLanguage { get; private set; } = AppConfig.DefaultLanguage;
+
     public override void Initialize()
     {
         AvaloniaXamlLoader.Load(this);
@@ -23,26 +34,69 @@ public partial class App : Application
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
             DisableAvaloniaDataAnnotationValidation();
+
+            // Startup order: apply the configured culture (and its RTL flow direction)
+            // and the theme BEFORE creating the main window.
+            CultureInfo culture = ResolveCulture(Services.Config.Language);
+            StartupLanguage = Services.Config.Language;
+            Resx.Culture = culture;
+            ApplyTheme(Services.Config.Theme);
+
+            var mainViewModel = new MainWindowViewModel(Services);
             desktop.MainWindow = new MainWindow
             {
-                DataContext = new MainWindowViewModel(),
+                DataContext = mainViewModel,
+
+                // RTL detection drives the whole window flow direction; the two
+                // supported languages are LTR, but the infrastructure stays in
+                // place for future languages.
+                FlowDirection = culture.TextInfo.IsRightToLeft
+                    ? FlowDirection.RightToLeft
+                    : FlowDirection.LeftToRight,
             };
 
             // Primary instance: serve launch commands forwarded by secondary instances.
-            Program.SingleInstance?.StartServer(command => HandleLaunchCommand(desktop, command));
+            Program.SingleInstance?.StartServer(command => HandleLaunchCommand(desktop, mainViewModel, command));
         }
 
         base.OnFrameworkInitializationCompleted();
     }
 
-    /// <summary>
+    /// <summary>Resolves the configured language to a culture, falling back to English.</summary>
-    /// Brings the main window to front for a forwarded launch command. Both
+    public static CultureInfo ResolveCulture(string language)
-    /// ShowMain and OpenWorkspace activate the window; switching to the
-    /// requested workspace lands together with the workspace UI.
-    /// </summary>
-    private static void HandleLaunchCommand(IClassicDesktopStyleApplicationLifetime desktop, LaunchCommand command)
     {
-        // IPC delivery happens on a background thread; window access must hop to the UI thread.
+        try
+        {
+            return new CultureInfo(language);
+        }
+        catch (CultureNotFoundException)
+        {
+            return new CultureInfo(AppConfig.DefaultLanguage);
+        }
+    }
+
+    /// <summary>Applies a theme selection immediately; Default follows the operating system.</summary>
+    public static void ApplyTheme(ThemeOption option)
+    {
+        if (Current is null)
+        {
+            return;
+        }
+        Current.RequestedThemeVariant = option switch
+        {
+            ThemeOption.Light => ThemeVariant.Light,
+            ThemeOption.Dark => ThemeVariant.Dark,
+            _ => ThemeVariant.Default,
+        };
+    }
+
+    /// <summary>Activates the window for a forwarded command; OpenWorkspace also switches to it.</summary>
+    private static void HandleLaunchCommand(
+        IClassicDesktopStyleApplicationLifetime desktop,
+        MainWindowViewModel mainViewModel,
+        LaunchCommand command)
+    {
+        // IPC delivery happens on a background thread; hop to the UI thread.
         Dispatcher.UIThread.Post(() =>
         {
             if (desktop.MainWindow is { } window)
@@ -50,6 +104,10 @@ public partial class App : Application
                 window.Show();
                 window.Activate();
             }
+            if (command is LaunchCommand.OpenWorkspace open)
+            {
+                mainViewModel.OpenWorkspaceFromLaunch(open.Path);
+            }
         });
     }
 

YKanBan/Assets/Locales/Resources.resx

@@ -51,4 +51,139 @@
   <data name="Export_TagsTableHeader" xml:space="preserve">
     <value>| Name | Color | Description | Usage |</value>
   </data>
+  <data name="App_Name" xml:space="preserve">
+    <value>YKanBan</value>
+  </data>
+  <data name="Common_Yes" xml:space="preserve">
+    <value>Yes</value>
+  </data>
+  <data name="Common_No" xml:space="preserve">
+    <value>No</value>
+  </data>
+  <data name="Common_Close" xml:space="preserve">
+    <value>Close</value>
+  </data>
+  <data name="Sidebar_Welcome" xml:space="preserve">
+    <value>Welcome</value>
+  </data>
+  <data name="Sidebar_OpenProject" xml:space="preserve">
+    <value>Open project…</value>
+  </data>
+  <data name="Sidebar_SortLabel" xml:space="preserve">
+    <value>Sort</value>
+  </data>
+  <data name="Sidebar_Sort_NameAsc" xml:space="preserve">
+    <value>Name A to Z</value>
+  </data>
+  <data name="Sidebar_Sort_NameDesc" xml:space="preserve">
+    <value>Name Z to A</value>
+  </data>
+  <data name="Sidebar_Sort_RecentlyUpdated" xml:space="preserve">
+    <value>Recently updated</value>
+  </data>
+  <data name="Sidebar_Settings" xml:space="preserve">
+    <value>Settings</value>
+  </data>
+  <data name="Sidebar_About" xml:space="preserve">
+    <value>About</value>
+  </data>
+  <data name="Sidebar_RemoveFromList" xml:space="preserve">
+    <value>Remove from list</value>
+  </data>
+  <data name="Welcome_Hint" xml:space="preserve">
+    <value>Open or create a workspace from the left.</value>
+  </data>
+  <data name="Dialog_InitializeTitle" xml:space="preserve">
+    <value>Initialize workspace?</value>
+  </data>
+  <data name="Dialog_InitializeMessage" xml:space="preserve">
+    <value>There is no .ykanban structure in "{0}". Initialize it here?</value>
+  </data>
+  <data name="Settings_Title" xml:space="preserve">
+    <value>Settings</value>
+  </data>
+  <data name="Settings_Language" xml:space="preserve">
+    <value>Language</value>
+  </data>
+  <data name="Settings_Language_RestartNotice" xml:space="preserve">
+    <value>Takes effect after restart</value>
+  </data>
+  <data name="Settings_LanguageEnglish" xml:space="preserve">
+    <value>English</value>
+  </data>
+  <data name="Settings_LanguageChinese" xml:space="preserve">
+    <value>简体中文</value>
+  </data>
+  <data name="Settings_Theme" xml:space="preserve">
+    <value>Theme</value>
+  </data>
+  <data name="Settings_ThemeLight" xml:space="preserve">
+    <value>Light</value>
+  </data>
+  <data name="Settings_ThemeDark" xml:space="preserve">
+    <value>Dark</value>
+  </data>
+  <data name="Settings_ThemeFollowSystem" xml:space="preserve">
+    <value>Follow system</value>
+  </data>
+  <data name="Settings_Confirmations" xml:space="preserve">
+    <value>Confirmations</value>
+  </data>
+  <data name="Settings_ConfirmDeleteCard" xml:space="preserve">
+    <value>Ask before deleting a card</value>
+  </data>
+  <data name="Settings_ConfirmDeleteColumn" xml:space="preserve">
+    <value>Ask before deleting a column</value>
+  </data>
+  <data name="Settings_ConfirmDeleteTag" xml:space="preserve">
+    <value>Ask before deleting a tag</value>
+  </data>
+  <data name="Settings_ConfirmDiscardEdit" xml:space="preserve">
+    <value>Ask before discarding card edits</value>
+  </data>
+  <data name="About_Title" xml:space="preserve">
+    <value>About</value>
+  </data>
+  <data name="About_Version" xml:space="preserve">
+    <value>Version {0}</value>
+  </data>
+  <data name="About_Repository" xml:space="preserve">
+    <value>Repository</value>
+  </data>
+  <data name="About_RepositoryUrl" xml:space="preserve">
+    <value>(to be filled)</value>
+  </data>
+  <data name="About_License" xml:space="preserve">
+    <value>License</value>
+  </data>
+  <data name="About_LicenseValue" xml:space="preserve">
+    <value>(to be filled)</value>
+  </data>
+  <data name="State_LockConflict_Title" xml:space="preserve">
+    <value>Workspace locked</value>
+  </data>
+  <data name="State_LockConflict_Detail" xml:space="preserve">
+    <value>The workspace is locked by another instance.</value>
+  </data>
+  <data name="State_NotInitialized_Title" xml:space="preserve">
+    <value>No workspace here</value>
+  </data>
+  <data name="State_NotInitialized_Detail" xml:space="preserve">
+    <value>The folder has no .ykanban structure.</value>
+  </data>
+  <data name="State_DirectoryMissing_Title" xml:space="preserve">
+    <value>Folder missing</value>
+  </data>
+  <data name="State_DirectoryMissing_Detail" xml:space="preserve">
+    <value>The folder does not exist on disk.</value>
+  </data>
+  <data name="State_SchemaVersion_Title" xml:space="preserve">
+    <value>Incompatible database</value>
+  </data>
+  <data name="State_SchemaVersion_Detail" xml:space="preserve">
+    <value>The workspace was written by a newer version.</value>
+  </data>
+  <data name="State_Unknown_Title" xml:space="preserve">
+    <value>Open failed</value>
+  </data>
 </root>

YKanBan/Assets/Locales/Resources.zh-Hans.resx

@@ -51,4 +51,139 @@
   <data name="Export_TagsTableHeader" xml:space="preserve">
     <value>| 名称 | 颜色 | 描述 | 使用数 |</value>
   </data>
+  <data name="App_Name" xml:space="preserve">
+    <value>YKanBan</value>
+  </data>
+  <data name="Common_Yes" xml:space="preserve">
+    <value>是</value>
+  </data>
+  <data name="Common_No" xml:space="preserve">
+    <value>否</value>
+  </data>
+  <data name="Common_Close" xml:space="preserve">
+    <value>关闭</value>
+  </data>
+  <data name="Sidebar_Welcome" xml:space="preserve">
+    <value>欢迎页</value>
+  </data>
+  <data name="Sidebar_OpenProject" xml:space="preserve">
+    <value>打开项目…</value>
+  </data>
+  <data name="Sidebar_SortLabel" xml:space="preserve">
+    <value>排序</value>
+  </data>
+  <data name="Sidebar_Sort_NameAsc" xml:space="preserve">
+    <value>名称 A 到 Z</value>
+  </data>
+  <data name="Sidebar_Sort_NameDesc" xml:space="preserve">
+    <value>名称 Z 到 A</value>
+  </data>
+  <data name="Sidebar_Sort_RecentlyUpdated" xml:space="preserve">
+    <value>最近更新</value>
+  </data>
+  <data name="Sidebar_Settings" xml:space="preserve">
+    <value>设置</value>
+  </data>
+  <data name="Sidebar_About" xml:space="preserve">
+    <value>关于</value>
+  </data>
+  <data name="Sidebar_RemoveFromList" xml:space="preserve">
+    <value>从列表移除</value>
+  </data>
+  <data name="Welcome_Hint" xml:space="preserve">
+    <value>从左侧打开或新建工作区。</value>
+  </data>
+  <data name="Dialog_InitializeTitle" xml:space="preserve">
+    <value>初始化工作区？</value>
+  </data>
+  <data name="Dialog_InitializeMessage" xml:space="preserve">
+    <value>“{0}”中不存在 .ykanban 数据。在此初始化？</value>
+  </data>
+  <data name="Settings_Title" xml:space="preserve">
+    <value>设置</value>
+  </data>
+  <data name="Settings_Language" xml:space="preserve">
+    <value>语言</value>
+  </data>
+  <data name="Settings_Language_RestartNotice" xml:space="preserve">
+    <value>重启后生效</value>
+  </data>
+  <data name="Settings_LanguageEnglish" xml:space="preserve">
+    <value>English</value>
+  </data>
+  <data name="Settings_LanguageChinese" xml:space="preserve">
+    <value>简体中文</value>
+  </data>
+  <data name="Settings_Theme" xml:space="preserve">
+    <value>主题</value>
+  </data>
+  <data name="Settings_ThemeLight" xml:space="preserve">
+    <value>浅色</value>
+  </data>
+  <data name="Settings_ThemeDark" xml:space="preserve">
+    <value>深色</value>
+  </data>
+  <data name="Settings_ThemeFollowSystem" xml:space="preserve">
+    <value>跟随系统</value>
+  </data>
+  <data name="Settings_Confirmations" xml:space="preserve">
+    <value>操作确认</value>
+  </data>
+  <data name="Settings_ConfirmDeleteCard" xml:space="preserve">
+    <value>删除卡片前确认</value>
+  </data>
+  <data name="Settings_ConfirmDeleteColumn" xml:space="preserve">
+    <value>删除列前确认</value>
+  </data>
+  <data name="Settings_ConfirmDeleteTag" xml:space="preserve">
+    <value>删除标签前确认</value>
+  </data>
+  <data name="Settings_ConfirmDiscardEdit" xml:space="preserve">
+    <value>放弃卡片编辑前确认</value>
+  </data>
+  <data name="About_Title" xml:space="preserve">
+    <value>关于</value>
+  </data>
+  <data name="About_Version" xml:space="preserve">
+    <value>版本 {0}</value>
+  </data>
+  <data name="About_Repository" xml:space="preserve">
+    <value>仓库</value>
+  </data>
+  <data name="About_RepositoryUrl" xml:space="preserve">
+    <value>（待填写）</value>
+  </data>
+  <data name="About_License" xml:space="preserve">
+    <value>许可证</value>
+  </data>
+  <data name="About_LicenseValue" xml:space="preserve">
+    <value>（待填写）</value>
+  </data>
+  <data name="State_LockConflict_Title" xml:space="preserve">
+    <value>工作区已被占用</value>
+  </data>
+  <data name="State_LockConflict_Detail" xml:space="preserve">
+    <value>该工作区正被另一实例锁定。</value>
+  </data>
+  <data name="State_NotInitialized_Title" xml:space="preserve">
+    <value>此处没有工作区</value>
+  </data>
+  <data name="State_NotInitialized_Detail" xml:space="preserve">
+    <value>该文件夹没有 .ykanban 数据。</value>
+  </data>
+  <data name="State_DirectoryMissing_Title" xml:space="preserve">
+    <value>文件夹不存在</value>
+  </data>
+  <data name="State_DirectoryMissing_Detail" xml:space="preserve">
+    <value>该文件夹在磁盘上不存在。</value>
+  </data>
+  <data name="State_SchemaVersion_Title" xml:space="preserve">
+    <value>数据库版本不兼容</value>
+  </data>
+  <data name="State_SchemaVersion_Detail" xml:space="preserve">
+    <value>该工作区由更新版本的程序创建。</value>
+  </data>
+  <data name="State_Unknown_Title" xml:space="preserve">
+    <value>打开失败</value>
+  </data>
 </root>

YKanBan/Program.cs

@@ -24,6 +24,10 @@ sealed class Program
 
         SingleInstance = singleInstance;
         BuildAvaloniaApp().StartWithClassicDesktopLifetime(args);
+
+        // Lifetime ended: persist the configuration once, then release the services.
+        App.Services.SaveConfiguration();
+        App.Services.Dispose();
     }
 
     public static AppBuilder BuildAvaloniaApp()

YKanBan/Services/AppServices.cs

@@ -0,0 +1,51 @@
+using YKanBan.Platform;
+using YKanBan.Storage.AppData;
+using YKanBan.Storage.Workspace;
+
+namespace YKanBan.Services;
+
+/// <summary>
+/// Composition root: owns the application-wide configuration, the global
+/// workspace registry and the workspace connection pool for the whole
+/// process lifetime. The configuration is persisted once at shutdown.
+/// </summary>
+public sealed class AppServices : IDisposable
+{
+    /// <summary>Maximum number of simultaneously open workspaces.</summary>
+    private const int PoolCapacity = 8;
+
+    /// <summary>Loads the configuration and opens the global services.</summary>
+    public AppServices()
+    {
+        ConfigStore = new AppConfigStore(AppDataPaths.AppConfigJsonPath);
+        Config = ConfigStore.Load();
+        Database = new AppDatabase(AppDataPaths.AppDatabasePath);
+        PathComparison = PathComparer.ForCurrentPlatform();
+        Pool = new WorkspaceConnectionPool(PoolCapacity, Database, PathComparison);
+    }
+
+    /// <summary>The mutable application configuration; persisted by <see cref="SaveConfiguration"/>.</summary>
+    public AppConfig Config { get; }
+
+    /// <summary>Store for app.json.</summary>
+    public AppConfigStore ConfigStore { get; }
+
+    /// <summary>Global workspace registry (app.db).</summary>
+    public AppDatabase Database { get; }
+
+    /// <summary>LRU pool of open workspace sessions.</summary>
+    public WorkspaceConnectionPool Pool { get; }
+
+    /// <summary>Platform path comparison rules.</summary>
+    public PathComparer PathComparison { get; }
+
+    /// <summary>Persists the configuration; called once at shutdown.</summary>
+    public void SaveConfiguration() => ConfigStore.Save(Config);
+
+    /// <summary>Releases the pool and the registry.</summary>
+    public void Dispose()
+    {
+        Pool.Dispose();
+        Database.Dispose();
+    }
+}

YKanBan/Storage/AppData/AppConfig.cs

@@ -130,13 +130,16 @@ public sealed class AppConfig
     /// <summary>Current configuration format version.</summary>
     public const int CurrentFormatVersion = 1;
 
+    /// <summary>The default UI language code.</summary>
+    public const string DefaultLanguage = "en";
+
     /// <summary>Configuration format version of this file.</summary>
     [JsonProperty("version")]
     public int Version { get; set; } = CurrentFormatVersion;
 
     /// <summary>UI language code: "en" (default) or "zh-Hans".</summary>
     [JsonProperty("language")]
-    public string Language { get; set; } = "en";
+    public string Language { get; set; } = DefaultLanguage;
 
     /// <summary>UI theme selection (default: follow the system).</summary>
     [JsonProperty("theme")]

YKanBan/Storage/AppData/AppDataPaths.cs

@@ -0,0 +1,15 @@
+namespace YKanBan.Storage.AppData;
+
+/// <summary>Well-known locations under the per-user application data folder.</summary>
+public static class AppDataPaths
+{
+    /// <summary>The per-user YKanBan application data folder.</summary>
+    public static string Directory =>
+        Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "YKanBan");
+
+    /// <summary>Full path of app.json.</summary>
+    public static string AppConfigJsonPath => Path.Combine(Directory, "app.json");
+
+    /// <summary>Full path of app.db.</summary>
+    public static string AppDatabasePath => Path.Combine(Directory, "app.db");
+}

YKanBan/ViewModels/Dialogs/AboutDialogViewModel.cs

@@ -0,0 +1,26 @@
+using System.Reflection;
+
+namespace YKanBan.ViewModels.Dialogs;
+
+/// <summary>The about dialog data: application identity and version.</summary>
+public sealed class AboutDialogViewModel : ViewModelBase
+{
+    /// <summary>Display name of the application.</summary>
+    public string ApplicationName => Resources.App_Name;
+
+    /// <summary>Localized "Version x.y.z" text.</summary>
+    public string VersionText => string.Format(
+        System.Globalization.CultureInfo.CurrentCulture,
+        Resources.About_Version,
+        AssemblyVersion);
+
+    /// <summary>Repository URL (from resources).</summary>
+    public string RepositoryUrl => Resources.About_RepositoryUrl;
+
+    /// <summary>License name (from resources).</summary>
+    public string LicenseValue => Resources.About_LicenseValue;
+
+    /// <summary>The assembly version, formatted as major.minor.patch.</summary>
+    public static string AssemblyVersion =>
+        Assembly.GetExecutingAssembly().GetName().Version?.ToString(3) ?? "0.0.0";
+}

YKanBan/ViewModels/Dialogs/ConfirmDialogViewModel.cs

@@ -0,0 +1,25 @@
+namespace YKanBan.ViewModels.Dialogs;
+
+/// <summary>A generic confirmation dialog: localized title, message and yes/no answers.</summary>
+public sealed class ConfirmDialogViewModel : ViewModelBase
+{
+    public ConfirmDialogViewModel(string title, string message)
+    {
+        Title = title;
+        Message = message;
+        ConfirmText = Resources.Common_Yes;
+        CancelText = Resources.Common_No;
+    }
+
+    /// <summary>Localized dialog heading.</summary>
+    public string Title { get; }
+
+    /// <summary>Localized message body.</summary>
+    public string Message { get; }
+
+    /// <summary>Label of the confirming button.</summary>
+    public string ConfirmText { get; }
+
+    /// <summary>Label of the cancelling button.</summary>
+    public string CancelText { get; }
+}

YKanBan/ViewModels/Dialogs/SettingsDialogViewModel.cs

@@ -0,0 +1,107 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using YKanBan.Services;
+using YKanBan.Storage.AppData;
+
+namespace YKanBan.ViewModels.Dialogs;
+
+/// <summary>
+/// The settings dialog: language (restart to apply), theme (applies
+/// immediately) and the four confirmation-dialog toggles. All changes write
+/// straight into the configuration, which persists at shutdown.
+/// </summary>
+public partial class SettingsDialogViewModel : ViewModelBase
+{
+    private readonly AppConfig _config;
+    private readonly string _startupLanguage;
+
+    public SettingsDialogViewModel(AppServices services)
+    {
+        _config = services.Config;
+        _startupLanguage = App.StartupLanguage;
+
+        Languages =
+        [
+            new OptionItem(AppConfig.DefaultLanguage, Resources.Settings_LanguageEnglish),
+            new OptionItem("zh-Hans", Resources.Settings_LanguageChinese),
+        ];
+        selectedLanguage = Languages.FirstOrDefault(option => (string)option.Value == _config.Language)
+            ?? Languages[0];
+
+        Themes =
+        [
+            new OptionItem(ThemeOption.Light, Resources.Settings_ThemeLight),
+            new OptionItem(ThemeOption.Dark, Resources.Settings_ThemeDark),
+            new OptionItem(ThemeOption.FollowSystem, Resources.Settings_ThemeFollowSystem),
+        ];
+        selectedTheme = Themes.FirstOrDefault(option => option.Value.Equals(_config.Theme)) ?? Themes[^1];
+
+        confirmDeleteCard = _config.Confirmations.DeleteCard;
+        confirmDeleteColumn = _config.Confirmations.DeleteColumn;
+        confirmDeleteTag = _config.Confirmations.DeleteTag;
+        confirmDiscardEdit = _config.Confirmations.DiscardEdit;
+    }
+
+    /// <summary>Available languages.</summary>
+    public IReadOnlyList<OptionItem> Languages { get; }
+
+    /// <summary>Available themes.</summary>
+    public IReadOnlyList<OptionItem> Themes { get; }
+
+    /// <summary>The selected language; takes effect after a restart.</summary>
+    [ObservableProperty]
+    private OptionItem? selectedLanguage;
+
+    /// <summary>The selected theme; applies immediately.</summary>
+    [ObservableProperty]
+    private OptionItem? selectedTheme;
+
+    /// <summary>Whether deleting a card asks for confirmation.</summary>
+    [ObservableProperty]
+    private bool confirmDeleteCard;
+
+    /// <summary>Whether deleting a column asks for confirmation.</summary>
+    [ObservableProperty]
+    private bool confirmDeleteColumn;
+
+    /// <summary>Whether deleting a tag asks for confirmation.</summary>
+    [ObservableProperty]
+    private bool confirmDeleteTag;
+
+    /// <summary>Whether discarding card edits asks for confirmation.</summary>
+    [ObservableProperty]
+    private bool confirmDiscardEdit;
+
+    /// <summary>True while the selected language differs from the one applied at startup.</summary>
+    [ObservableProperty]
+    private bool restartNoticeVisible;
+
+    /// <summary>Stores the language and refreshes the restart notice.</summary>
+    partial void OnSelectedLanguageChanged(OptionItem? value)
+    {
+        if (value is null)
+        {
+            return;
+        }
+        _config.Language = (string)value.Value;
+        RestartNoticeVisible = _config.Language != _startupLanguage;
+    }
+
+    /// <summary>Stores the theme and applies it immediately.</summary>
+    partial void OnSelectedThemeChanged(OptionItem? value)
+    {
+        if (value is null)
+        {
+            return;
+        }
+        _config.Theme = (ThemeOption)value.Value;
+        App.ApplyTheme(_config.Theme);
+    }
+
+    partial void OnConfirmDeleteCardChanged(bool value) => _config.Confirmations.DeleteCard = value;
+
+    partial void OnConfirmDeleteColumnChanged(bool value) => _config.Confirmations.DeleteColumn = value;
+
+    partial void OnConfirmDeleteTagChanged(bool value) => _config.Confirmations.DeleteTag = value;
+
+    partial void OnConfirmDiscardEditChanged(bool value) => _config.Confirmations.DiscardEdit = value;
+}

YKanBan/ViewModels/Interaction.cs

@@ -0,0 +1,26 @@
+namespace YKanBan.ViewModels;
+
+/// <summary>Input placeholder for interactions that carry no meaningful input.</summary>
+public readonly record struct Unit;
+
+/// <summary>
+/// A view-model side request that the owning view fulfils through a
+/// registered handler (dialogs, pickers) — the classic MVVM interaction
+/// pattern, implemented locally without extra dependencies.
+/// </summary>
+/// <typeparam name="TInput">The request payload.</typeparam>
+/// <typeparam name="TOutput">The handler's answer.</typeparam>
+public sealed class Interaction<TInput, TOutput>
+{
+    private Func<TInput, Task<TOutput>>? _handler;
+
+    /// <summary>Registers the single handler; the view calls this once.</summary>
+    public void RegisterHandler(Func<TInput, Task<TOutput>> handler) => _handler = handler;
+
+    /// <summary>Invokes the registered handler.</summary>
+    /// <exception cref="InvalidOperationException">No handler has been registered.</exception>
+    public Task<TOutput> Handle(TInput input) =>
+        _handler is null
+            ? throw new InvalidOperationException("No handler registered for this interaction.")
+            : _handler(input);
+}

YKanBan/ViewModels/MainWindowViewModel.cs

@@ -1,5 +1,103 @@
-namespace YKanBan.ViewModels;
+using CommunityToolkit.Mvvm.ComponentModel;
+using YKanBan.Services;
+using YKanBan.Storage;
+using YKanBan.Storage.Workspace;
+using YKanBan.ViewModels.Pages;
 
+namespace YKanBan.ViewModels;
+
+/// <summary>
+/// Root view model: owns the sidebar and the current content page (welcome,
+/// an open workspace, or a failure state page).
+/// </summary>
 public partial class MainWindowViewModel : ViewModelBase
 {
+    public MainWindowViewModel(AppServices services)
+    {
+        Services = services;
+        Sidebar = new SidebarViewModel(this, services);
+        CurrentContent = new WelcomePageViewModel();
+    }
+
+    /// <summary>The composition root.</summary>
+    public AppServices Services { get; }
+
+    /// <summary>The workspace sidebar.</summary>
+    public SidebarViewModel Sidebar { get; }
+
+    /// <summary>The currently displayed content page.</summary>
+    [ObservableProperty]
+    private object? currentContent;
+
+    /// <summary>Shows the welcome page (no workspace active).</summary>
+    public void ShowWelcome()
+    {
+        CurrentContent = new WelcomePageViewModel();
+    }
+
+    /// <summary>
+    /// Opens (or switches to) a workspace from the UI flow: a plain folder
+    /// prompts for initialization before opening.
+    /// </summary>
+    public async Task OpenWorkspaceWithInitializePromptAsync(string folderPath)
+    {
+        string canonical = Services.PathComparison.Normalize(folderPath);
+
+        if (!WorkspaceInitializer.IsWorkspace(canonical))
+        {
+            if (!Directory.Exists(canonical))
+            {
+                ShowFailure(Resources.State_DirectoryMissing_Title, Resources.State_DirectoryMissing_Detail);
+                return;
+            }
+
+            bool confirmed = await Sidebar.ConfirmInitialize.Handle(canonical);
+            if (!confirmed)
+            {
+                return;
+            }
+            WorkspaceInitializer.Initialize(canonical);
+            WorkspacePreset.SeedColumns(canonical);
+        }
+
+        TryOpenWorkspaceSession(canonical);
+    }
+
+    /// <summary>Opens (or switches to) a workspace without any initialization prompt (IPC entry).</summary>
+    public void OpenWorkspaceFromLaunch(string folderPath)
+    {
+        TryOpenWorkspaceSession(Services.PathComparison.Normalize(folderPath));
+    }
+
+    /// <summary>Opens the session through the pool; typed failures map to localized state pages.</summary>
+    public void TryOpenWorkspaceSession(string canonicalPath)
+    {
+        try
+        {
+            WorkspaceSession session = Services.Pool.Open(canonicalPath);
+            CurrentContent = new WorkspacePageViewModel(session);
+            Sidebar.RebuildWorkspaceList();
+        }
+        catch (Exception ex)
+        {
+            (string title, string detail) = DescribeOpenFailure(ex);
+            ShowFailure(title, detail);
+        }
+    }
+
+    /// <summary>Displays a localized failure state page.</summary>
+    private void ShowFailure(string title, string detail)
+    {
+        CurrentContent = new MessagePageViewModel(title, detail);
+    }
+
+    /// <summary>Maps an open failure to localized title/detail text by exception type.</summary>
+    private static (string Title, string Detail) DescribeOpenFailure(Exception exception) => exception switch
+    {
+        WorkspaceLockException => (Resources.State_LockConflict_Title, Resources.State_LockConflict_Detail),
+        WorkspaceNotInitializedException => (Resources.State_NotInitialized_Title, Resources.State_NotInitialized_Detail),
+        WorkspaceDirectoryMissingException => (Resources.State_DirectoryMissing_Title, Resources.State_DirectoryMissing_Detail),
+        SchemaVersionException => (Resources.State_SchemaVersion_Title, Resources.State_SchemaVersion_Detail),
+        _ => (Resources.State_Unknown_Title, exception.Message),
+    };
 }

YKanBan/ViewModels/OptionItem.cs

@@ -0,0 +1,6 @@
+namespace YKanBan.ViewModels;
+
+/// <summary>A selectable option item for combo boxes: a value plus its localized label.</summary>
+/// <param name="Value">The backing value (enum value or language code).</param>
+/// <param name="Label">The localized display label.</param>
+public sealed record OptionItem(object Value, string Label);

YKanBan/ViewModels/Pages/MessagePageViewModel.cs

@@ -0,0 +1,17 @@
+namespace YKanBan.ViewModels.Pages;
+
+/// <summary>A failure state page: a localized title with a detail line.</summary>
+public sealed class MessagePageViewModel : ViewModelBase
+{
+    public MessagePageViewModel(string title, string detail)
+    {
+        Title = title;
+        Detail = detail;
+    }
+
+    /// <summary>Localized failure heading.</summary>
+    public string Title { get; }
+
+    /// <summary>Localized failure explanation.</summary>
+    public string Detail { get; }
+}

YKanBan/ViewModels/Pages/WelcomePageViewModel.cs

@@ -0,0 +1,6 @@
+namespace YKanBan.ViewModels.Pages;
+
+/// <summary>The welcome page: application identity plus a hint to open a workspace.</summary>
+public sealed class WelcomePageViewModel : ViewModelBase
+{
+}

YKanBan/ViewModels/Pages/WorkspacePageViewModel.cs

@@ -0,0 +1,22 @@
+using YKanBan.Storage.Workspace;
+
+namespace YKanBan.ViewModels.Pages;
+
+/// <summary>
+/// An open workspace page. The board, tags and search views mount here in
+/// the later UI milestones; the frame shows the workspace identity for now.
+/// </summary>
+public sealed class WorkspacePageViewModel : ViewModelBase
+{
+    public WorkspacePageViewModel(WorkspaceSession session)
+    {
+        FullPath = session.FolderPath;
+        Name = Path.GetFileName(session.FolderPath);
+    }
+
+    /// <summary>Canonical workspace folder path.</summary>
+    public string FullPath { get; }
+
+    /// <summary>Display name: the folder name.</summary>
+    public string Name { get; }
+}

YKanBan/ViewModels/SidebarViewModel.cs

@@ -0,0 +1,140 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using YKanBan.Services;
+using YKanBan.Storage.AppData;
+using YKanBan.Storage.Workspace;
+using YKanBan.ViewModels.Pages;
+
+namespace YKanBan.ViewModels;
+
+/// <summary>
+/// The sidebar: welcome and open-project buttons, the persistent workspace
+/// list with its sort options, and the settings/about entries at the bottom.
+/// </summary>
+public partial class SidebarViewModel : ViewModelBase
+{
+    private readonly MainWindowViewModel _owner;
+    private readonly AppServices _services;
+
+    public SidebarViewModel(MainWindowViewModel owner, AppServices services)
+    {
+        _owner = owner;
+        _services = services;
+
+        SortOptions =
+        [
+            new OptionItem(SidebarSortOption.NameAsc, Resources.Sidebar_Sort_NameAsc),
+            new OptionItem(SidebarSortOption.NameDesc, Resources.Sidebar_Sort_NameDesc),
+            new OptionItem(SidebarSortOption.RecentlyUpdated, Resources.Sidebar_Sort_RecentlyUpdated),
+        ];
+        selectedSort = SortOptions.Single(option => option.Value.Equals(services.Config.Sort.Sidebar));
+
+        RebuildWorkspaceList();
+    }
+
+    /// <summary>Known workspaces in display order.</summary>
+    public ObservableCollection<WorkspaceItemViewModel> Workspaces { get; } = [];
+
+    /// <summary>The available list sort modes.</summary>
+    public IReadOnlyList<OptionItem> SortOptions { get; }
+
+    /// <summary>Asks the view for a folder via the system folder picker; null when cancelled.</summary>
+    public Interaction<Unit, string?> PickFolder { get; } = new();
+
+    /// <summary>Asks the view to confirm initializing a plain folder as a workspace.</summary>
+    public Interaction<string, bool> ConfirmInitialize { get; } = new();
+    /// <summary>The selected list sort mode; persisted with the configuration.</summary>
+    [ObservableProperty]
+    private OptionItem? selectedSort;
+
+    /// <summary>Shows the welcome page.</summary>
+    [RelayCommand]
+    private void ShowWelcome()
+    {
+        _owner.ShowWelcome();
+    }
+
+    /// <summary>Picks a folder and opens it as a workspace (offering initialization).</summary>
+    [RelayCommand]
+    private async Task OpenProjectAsync()
+    {
+        string? folder = await PickFolder.Handle(default);
+        if (folder is null)
+        {
+            return;
+        }
+        await _owner.OpenWorkspaceWithInitializePromptAsync(folder);
+    }
+
+    /// <summary>Rebuilds the list from the persistent registry, marking open workspaces.</summary>
+    public void RebuildWorkspaceList()
+    {
+        Workspaces.Clear();
+        foreach (WorkspaceRecord record in _services.Database.GetWorkspaces())
+        {
+            bool isOpen = _services.Pool.Find(record.Path) is not null;
+            Workspaces.Add(new WorkspaceItemViewModel(this, record.Path, Path.GetFileName(record.Path), record.LastEditedAt, isOpen));
+        }
+        ReorderWorkspaceList();
+    }
+
+    /// <summary>Opens a workspace when its sidebar entry is activated.</summary>
+    public void OpenWorkspace(WorkspaceItemViewModel item)
+    {
+        _owner.TryOpenWorkspaceSession(item.FullPath);
+    }
+
+    /// <summary>Releases the workspace resources and forgets its sidebar entry.</summary>
+    public void RemoveWorkspace(WorkspaceItemViewModel item)
+    {
+        _services.Pool.Remove(item.FullPath);
+        RebuildWorkspaceList();
+
+        // Removing the active workspace falls back to the welcome page.
+        if (_owner.CurrentContent is WorkspacePageViewModel active && active.FullPath == item.FullPath)
+        {
+            _owner.ShowWelcome();
+        }
+    }
+
+    /// <summary>Applies the selected sort mode to the list in place.</summary>
+    partial void OnSelectedSortChanged(OptionItem? value)
+    {
+        if (value is null)
+        {
+            return;
+        }
+        _services.Config.Sort.Sidebar = (SidebarSortOption)value.Value;
+        ReorderWorkspaceList();
+    }
+
+    /// <summary>Sorts the workspace collection by the current mode.</summary>
+    private void ReorderWorkspaceList()
+    {
+        if (SelectedSort?.Value is not SidebarSortOption mode)
+        {
+            return;
+        }
+
+        Comparison<WorkspaceItemViewModel> comparison = mode switch
+        {
+            SidebarSortOption.NameAsc => (a, b) => string.Compare(a.Name, b.Name, StringComparison.OrdinalIgnoreCase),
+            SidebarSortOption.NameDesc => (a, b) => string.Compare(b.Name, a.Name, StringComparison.OrdinalIgnoreCase),
+            SidebarSortOption.RecentlyUpdated => (a, b) => b.LastEditedAt.CompareTo(a.LastEditedAt),
+            _ => (a, b) => 0,
+        };
+
+        // Move each item into its sorted position (in-place keeps bindings alive).
+        List<WorkspaceItemViewModel> ordered = Workspaces.ToList();
+        ordered.Sort(comparison);
+        for (int index = 0; index < ordered.Count; index++)
+        {
+            int current = Workspaces.IndexOf(ordered[index]);
+            if (current != index)
+            {
+                Workspaces.Move(current, index);
+            }
+        }
+    }
+}

YKanBan/ViewModels/WorkspaceItemViewModel.cs

@@ -0,0 +1,46 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+
+namespace YKanBan.ViewModels;
+
+/// <summary>One sidebar workspace entry.</summary>
+public partial class WorkspaceItemViewModel : ViewModelBase
+{
+    private readonly SidebarViewModel _owner;
+
+    public WorkspaceItemViewModel(SidebarViewModel owner, string fullPath, string name, long lastEditedAt, bool isOpen)
+    {
+        _owner = owner;
+        FullPath = fullPath;
+        Name = name;
+        LastEditedAt = lastEditedAt;
+        IsOpen = isOpen;
+    }
+
+    /// <summary>Canonical workspace folder path.</summary>
+    public string FullPath { get; }
+
+    /// <summary>Display name: the folder name.</summary>
+    public string Name { get; }
+
+    /// <summary>Last edit time in Unix seconds, used by the "recently updated" sort.</summary>
+    public long LastEditedAt { get; }
+
+    /// <summary>Whether the workspace currently has an open session.</summary>
+    [ObservableProperty]
+    private bool isOpen;
+
+    /// <summary>Opens (or switches to) this workspace.</summary>
+    [RelayCommand]
+    private void Open()
+    {
+        _owner.OpenWorkspace(this);
+    }
+
+    /// <summary>Releases the workspace resources and removes the sidebar entry.</summary>
+    [RelayCommand]
+    private void Remove()
+    {
+        _owner.RemoveWorkspace(this);
+    }
+}

YKanBan/Views/Dialogs/AboutDialog.axaml

@@ -0,0 +1,30 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:YKanBan.ViewModels.Dialogs"
+        xmlns:lang="using:YKanBan"
+        x:Class="YKanBan.Views.Dialogs.AboutDialog"
+        x:DataType="vm:AboutDialogViewModel"
+        Title="{x:Static lang:Resources.About_Title}"
+        WindowStartupLocation="CenterOwner"
+        SizeToContent="Height" Width="380" CanResize="False"
+        ShowInTaskbar="False">
+
+    <StackPanel Margin="20" Spacing="10">
+        <TextBlock Text="{Binding ApplicationName}" FontSize="22" FontWeight="Bold"/>
+
+        <TextBlock Text="{Binding VersionText}" Opacity="0.8"/>
+
+        <Grid ColumnDefinitions="Auto,*" Margin="0,6,0,0">
+            <TextBlock Grid.Column="0" Text="{x:Static lang:Resources.About_Repository}" Opacity="0.7" Margin="0,0,8,0"/>
+            <TextBlock Grid.Column="1" Text="{Binding RepositoryUrl}" TextWrapping="Wrap"/>
+        </Grid>
+
+        <Grid ColumnDefinitions="Auto,*">
+            <TextBlock Grid.Column="0" Text="{x:Static lang:Resources.About_License}" Opacity="0.7" Margin="0,0,8,0"/>
+            <TextBlock Grid.Column="1" Text="{Binding LicenseValue}"/>
+        </Grid>
+
+        <Button Content="{x:Static lang:Resources.Common_Close}" IsCancel="True"
+                HorizontalAlignment="Right" MinWidth="90" Margin="0,8,0,0"/>
+    </StackPanel>
+</Window>

YKanBan/Views/Dialogs/AboutDialog.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace YKanBan.Views.Dialogs;
+
+public partial class AboutDialog : Window
+{
+    public AboutDialog()
+    {
+        InitializeComponent();
+    }
+}

YKanBan/Views/Dialogs/ConfirmDialog.axaml

@@ -0,0 +1,19 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:YKanBan.ViewModels.Dialogs"
+        x:Class="YKanBan.Views.Dialogs.ConfirmDialog"
+        x:DataType="vm:ConfirmDialogViewModel"
+        Title="{Binding Title}"
+        WindowStartupLocation="CenterOwner"
+        SizeToContent="Height" Width="440" CanResize="False"
+        ShowInTaskbar="False">
+
+    <StackPanel Margin="20" Spacing="16">
+        <TextBlock Text="{Binding Message}" TextWrapping="Wrap"/>
+
+        <StackPanel Orientation="Horizontal" Spacing="8" HorizontalAlignment="Right">
+            <Button Content="{Binding CancelText}" MinWidth="90" IsCancel="True" Click="OnCancelClick"/>
+            <Button Content="{Binding ConfirmText}" MinWidth="90" IsDefault="True" Classes="Primary" Click="OnConfirmClick"/>
+        </StackPanel>
+    </StackPanel>
+</Window>

YKanBan/Views/Dialogs/ConfirmDialog.axaml.cs

@@ -0,0 +1,16 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+
+namespace YKanBan.Views.Dialogs;
+
+public partial class ConfirmDialog : Window
+{
+    public ConfirmDialog()
+    {
+        InitializeComponent();
+    }
+
+    private void OnConfirmClick(object? sender, RoutedEventArgs e) => Close(true);
+
+    private void OnCancelClick(object? sender, RoutedEventArgs e) => Close(false);
+}

YKanBan/Views/Dialogs/SettingsDialog.axaml

@@ -0,0 +1,50 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:YKanBan.ViewModels.Dialogs"
+        xmlns:vmBase="using:YKanBan.ViewModels"
+        xmlns:lang="using:YKanBan"
+        x:Class="YKanBan.Views.Dialogs.SettingsDialog"
+        x:DataType="vm:SettingsDialogViewModel"
+        Title="{x:Static lang:Resources.Settings_Title}"
+        WindowStartupLocation="CenterOwner"
+        SizeToContent="Height" Width="440" CanResize="False"
+        ShowInTaskbar="False">
+
+    <StackPanel Margin="20" Spacing="14">
+        <StackPanel Spacing="4">
+            <TextBlock Text="{x:Static lang:Resources.Settings_Language}"/>
+            <ComboBox ItemsSource="{Binding Languages}" SelectedItem="{Binding SelectedLanguage}" HorizontalAlignment="Stretch">
+                <ComboBox.ItemTemplate>
+                    <DataTemplate x:DataType="vmBase:OptionItem">
+                        <TextBlock Text="{Binding Label}"/>
+                    </DataTemplate>
+                </ComboBox.ItemTemplate>
+            </ComboBox>
+            <TextBlock Text="{x:Static lang:Resources.Settings_Language_RestartNotice}"
+                       IsVisible="{Binding RestartNoticeVisible}"
+                       FontStyle="Italic" Opacity="0.7"/>
+        </StackPanel>
+
+        <StackPanel Spacing="4">
+            <TextBlock Text="{x:Static lang:Resources.Settings_Theme}"/>
+            <ComboBox ItemsSource="{Binding Themes}" SelectedItem="{Binding SelectedTheme}" HorizontalAlignment="Stretch">
+                <ComboBox.ItemTemplate>
+                    <DataTemplate x:DataType="vmBase:OptionItem">
+                        <TextBlock Text="{Binding Label}"/>
+                    </DataTemplate>
+                </ComboBox.ItemTemplate>
+            </ComboBox>
+        </StackPanel>
+
+        <StackPanel Spacing="6">
+            <TextBlock Text="{x:Static lang:Resources.Settings_Confirmations}"/>
+            <CheckBox Content="{x:Static lang:Resources.Settings_ConfirmDeleteCard}" IsChecked="{Binding ConfirmDeleteCard}"/>
+            <CheckBox Content="{x:Static lang:Resources.Settings_ConfirmDeleteColumn}" IsChecked="{Binding ConfirmDeleteColumn}"/>
+            <CheckBox Content="{x:Static lang:Resources.Settings_ConfirmDeleteTag}" IsChecked="{Binding ConfirmDeleteTag}"/>
+            <CheckBox Content="{x:Static lang:Resources.Settings_ConfirmDiscardEdit}" IsChecked="{Binding ConfirmDiscardEdit}"/>
+        </StackPanel>
+
+        <Button Content="{x:Static lang:Resources.Common_Close}" IsCancel="True"
+                HorizontalAlignment="Right" MinWidth="90"/>
+    </StackPanel>
+</Window>

YKanBan/Views/Dialogs/SettingsDialog.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace YKanBan.Views.Dialogs;
+
+public partial class SettingsDialog : Window
+{
+    public SettingsDialog()
+    {
+        InitializeComponent();
+    }
+}

YKanBan/Views/MainWindow.axaml

@@ -1,15 +1,107 @@
 <Window xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="using:YKanBan.ViewModels"
+        xmlns:pages="using:YKanBan.Views.Pages"
+        xmlns:lang="using:YKanBan"
+        xmlns:iconPacks="using:IconPacks.Avalonia.Lucide"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+        mc:Ignorable="d" d:DesignWidth="1000" d:DesignHeight="640"
         x:Class="YKanBan.Views.MainWindow"
         x:DataType="vm:MainWindowViewModel"
-        Title="YKanBan">
+        Icon="/Assets/avalonia-logo.ico"
+        Title="{x:Static lang:Resources.App_Name}"
+        Width="1000" Height="640" MinWidth="720" MinHeight="480">
 
-    <Design.DataContext>
+    <Grid ColumnDefinitions="260,*">
-        <vm:MainWindowViewModel/>
+        <!-- Sidebar -->
-    </Design.DataContext>
+        <Border Grid.Column="0"
+                Background="{DynamicResource SidebarBackgroundBrush}"
+                BorderBrush="{DynamicResource SidebarBorderBrush}"
+                BorderThickness="0,0,1,0"
+                Padding="8">
+            <Grid RowDefinitions="Auto,Auto,Auto,Auto,*,Auto">
+                <Button Grid.Row="0" Margin="0,8,0,4" HorizontalAlignment="Stretch" HorizontalContentAlignment="Left"
+                        Command="{Binding Sidebar.ShowWelcomeCommand}">
+                    <StackPanel Orientation="Horizontal" Spacing="8">
+                        <iconPacks:PackIconLucide Kind="House"/>
+                        <TextBlock Text="{x:Static lang:Resources.Sidebar_Welcome}"/>
+                    </StackPanel>
+                </Button>
 
+                <Button Grid.Row="1" Margin="0,4" HorizontalAlignment="Stretch" HorizontalContentAlignment="Left"
+                        Command="{Binding Sidebar.OpenProjectCommand}">
+                    <StackPanel Orientation="Horizontal" Spacing="8">
+                        <iconPacks:PackIconLucide Kind="FolderPlus"/>
+                        <TextBlock Text="{x:Static lang:Resources.Sidebar_OpenProject}"/>
+                    </StackPanel>
+                </Button>
+
+                <TextBlock Grid.Row="2" Margin="8,12,0,4" Opacity="0.65"
+                           Text="{x:Static lang:Resources.Sidebar_SortLabel}"/>
+                <ComboBox Grid.Row="3" Margin="0,0,0,8" HorizontalAlignment="Stretch"
+                          ItemsSource="{Binding Sidebar.SortOptions}"
+                          SelectedItem="{Binding Sidebar.SelectedSort}">
+                    <ComboBox.ItemTemplate>
+                        <DataTemplate x:DataType="vm:OptionItem">
+                            <TextBlock Text="{Binding Label}"/>
+                        </DataTemplate>
+                    </ComboBox.ItemTemplate>
+                </ComboBox>
+
+                <ListBox Grid.Row="4" ItemsSource="{Binding Sidebar.Workspaces}">
+                    <ListBox.ItemTemplate>
+                        <DataTemplate x:DataType="vm:WorkspaceItemViewModel">
+                            <Button Margin="0,1" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch"
+                                    Command="{Binding OpenCommand}">
+                                <Button.ContextMenu>
+                                    <ContextMenu>
+                                        <MenuItem Header="{x:Static lang:Resources.Sidebar_RemoveFromList}"
+                                                  Command="{Binding RemoveCommand}"/>
+                                    </ContextMenu>
+                                </Button.ContextMenu>
+                                <Grid ColumnDefinitions="*,Auto">
+                                    <TextBlock Grid.Column="0" Text="{Binding Name}" TextTrimming="CharacterEllipsis"/>
+                                    <TextBlock Grid.Column="1" Text="●" Opacity="0.55"
+                                               IsVisible="{Binding IsOpen}"/>
+                                </Grid>
+                            </Button>
+                        </DataTemplate>
+                    </ListBox.ItemTemplate>
+                </ListBox>
+
+                <StackPanel Grid.Row="5" Orientation="Horizontal" Spacing="8" Margin="0,8">
+                    <Button Click="OnSettingsClick">
+                        <StackPanel Orientation="Horizontal" Spacing="8">
+                            <iconPacks:PackIconLucide Kind="Settings"/>
+                            <TextBlock Text="{x:Static lang:Resources.Sidebar_Settings}"/>
+                        </StackPanel>
+                    </Button>
+                    <Button Click="OnAboutClick">
+                        <StackPanel Orientation="Horizontal" Spacing="8">
+                            <iconPacks:PackIconLucide Kind="Info"/>
+                            <TextBlock Text="{x:Static lang:Resources.Sidebar_About}"/>
+                        </StackPanel>
+                    </Button>
+                </StackPanel>
+            </Grid>
+        </Border>
+
+        <!-- Content area -->
+        <Border Grid.Column="1">
+            <ContentControl Content="{Binding CurrentContent}">
+                <ContentControl.DataTemplates>
+                    <DataTemplate x:DataType="vm:Pages.WelcomePageViewModel">
+                        <pages:WelcomePage/>
+                    </DataTemplate>
+                    <DataTemplate x:DataType="vm:Pages.WorkspacePageViewModel">
+                        <pages:WorkspacePage/>
+                    </DataTemplate>
+                    <DataTemplate x:DataType="vm:Pages.MessagePageViewModel">
+                        <pages:MessagePage/>
+                    </DataTemplate>
+                </ContentControl.DataTemplates>
+            </ContentControl>
+        </Border>
+    </Grid>
 </Window>

YKanBan/Views/MainWindow.axaml.cs

@@ -1,11 +1,76 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
 using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Platform.Storage;
+using YKanBan.ViewModels;
+using YKanBan.ViewModels.Dialogs;
+using YKanBan.Views.Dialogs;
+using Resx = YKanBan.Resources;
 
 namespace YKanBan.Views;
 
 public partial class MainWindow : Window
 {
+    private bool _interactionsRegistered;
+
     public MainWindow()
     {
         InitializeComponent();
     }
+
+    protected override void OnDataContextChanged(EventArgs e)
+    {
+        base.OnDataContextChanged(e);
+        if (DataContext is MainWindowViewModel viewModel && !_interactionsRegistered)
+        {
+            _interactionsRegistered = true;
+            RegisterInteractionHandlers(viewModel);
+        }
+    }
+
+    /// <summary>Wires the view model's dialog interactions to this window.</summary>
+    private void RegisterInteractionHandlers(MainWindowViewModel viewModel)
+    {
+        viewModel.Sidebar.PickFolder.RegisterHandler(async _ =>
+        {
+            IReadOnlyList<IStorageFolder> folders = await StorageProvider.OpenFolderPickerAsync(
+                new FolderPickerOpenOptions
+                {
+                    Title = Resx.Sidebar_OpenProject,
+                    AllowMultiple = false,
+                });
+            return folders.Count == 1 ? folders[0].TryGetLocalPath() : null;
+        });
+
+        viewModel.Sidebar.ConfirmInitialize.RegisterHandler(async folderPath =>
+        {
+            var dialog = new ConfirmDialog
+            {
+                DataContext = new ConfirmDialogViewModel(
+                    Resx.Dialog_InitializeTitle,
+                    string.Format(CultureInfo.CurrentCulture, Resx.Dialog_InitializeMessage, folderPath)),
+            };
+            return await dialog.ShowDialog<bool>(this);
+        });
+    }
+
+    private async void OnSettingsClick(object? sender, RoutedEventArgs e)
+    {
+        var dialog = new SettingsDialog
+        {
+            DataContext = new SettingsDialogViewModel(App.Services),
+        };
+        await dialog.ShowDialog(this);
+    }
+
+    private async void OnAboutClick(object? sender, RoutedEventArgs e)
+    {
+        var dialog = new AboutDialog
+        {
+            DataContext = new AboutDialogViewModel(),
+        };
+        await dialog.ShowDialog(this);
+    }
 }

YKanBan/Views/Pages/MessagePage.axaml

@@ -0,0 +1,10 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:YKanBan.ViewModels.Pages"
+             x:Class="YKanBan.Views.Pages.MessagePage"
+             x:DataType="vm:MessagePageViewModel">
+    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" Spacing="10">
+        <TextBlock Text="{Binding Title}" FontSize="20" FontWeight="SemiBold" HorizontalAlignment="Center"/>
+        <TextBlock Text="{Binding Detail}" Opacity="0.7" HorizontalAlignment="Center" TextWrapping="Wrap"/>
+    </StackPanel>
+</UserControl>

YKanBan/Views/Pages/MessagePage.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace YKanBan.Views.Pages;
+
+public partial class MessagePage : UserControl
+{
+    public MessagePage()
+    {
+        InitializeComponent();
+    }
+}

YKanBan/Views/Pages/WelcomePage.axaml

@@ -0,0 +1,11 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:lang="using:YKanBan"
+             x:Class="YKanBan.Views.Pages.WelcomePage">
+    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" Spacing="12">
+        <TextBlock Text="{x:Static lang:Resources.App_Name}" FontSize="32" FontWeight="Bold"
+                   HorizontalAlignment="Center"/>
+        <TextBlock Text="{x:Static lang:Resources.Welcome_Hint}" Opacity="0.65"
+                   HorizontalAlignment="Center"/>
+    </StackPanel>
+</UserControl>

YKanBan/Views/Pages/WelcomePage.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace YKanBan.Views.Pages;
+
+public partial class WelcomePage : UserControl
+{
+    public WelcomePage()
+    {
+        InitializeComponent();
+    }
+}

YKanBan/Views/Pages/WorkspacePage.axaml

@@ -0,0 +1,10 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:YKanBan.ViewModels.Pages"
+             x:Class="YKanBan.Views.Pages.WorkspacePage"
+             x:DataType="vm:WorkspacePageViewModel">
+    <StackPanel Margin="24,20" Spacing="6">
+        <TextBlock Text="{Binding Name}" FontSize="22" FontWeight="SemiBold"/>
+        <TextBlock Text="{Binding FullPath}" Opacity="0.6" FontSize="12"/>
+    </StackPanel>
+</UserControl>

YKanBan/Views/Pages/WorkspacePage.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace YKanBan.Views.Pages;
+
+public partial class WorkspacePage : UserControl
+{
+    public WorkspacePage()
+    {
+        InitializeComponent();
+    }
+}