fix(view-locator): show the missing-view placeholder through a resource key

PLAN 8.1 forbids hard-coded UI text; the template's ViewLocator still
built "Not Found: " in code.

YKanBan/Assets/Locales/Resources.resx

@@ -343,6 +343,9 @@
   <data name="Error_Operation_Message" xml:space="preserve">
     <value>The change could not be written to the workspace. The board shows the stored state.</value>
   </data>
+  <data name="Error_ViewNotFound" xml:space="preserve">
+    <value>View not found: {0}</value>
+  </data>
   <data name="Error_Read_Title" xml:space="preserve">
     <value>Reading failed</value>
   </data>

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

@@ -343,6 +343,9 @@
   <data name="Error_Operation_Message" xml:space="preserve">
     <value>更改未能写入工作区，看板显示的是已保存的状态。</value>
   </data>
+  <data name="Error_ViewNotFound" xml:space="preserve">
+    <value>找不到视图：{0}</value>
+  </data>
   <data name="Error_Read_Title" xml:space="preserve">
     <value>读取失败</value>
   </data>

YKanBan/ViewLocator.cs

@@ -1,31 +1,34 @@
-using System;
 using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using YKanBan.ViewModels;
 
 namespace YKanBan;
 
+/// <summary>
+/// Resolves the view of a view model by naming convention: the type name with
+/// "ViewModel" replaced by "View". A missing view is a programming error; it
+/// shows a localized placeholder naming the type that was looked for.
+/// </summary>
 public class ViewLocator : IDataTemplate
 {
-
+    /// <inheritdoc/>
     public Control? Build(object? param)
     {
         if (param is null)
+        {
             return null;
-        
-        var name = param.GetType().FullName!.Replace("ViewModel", "View", StringComparison.Ordinal);
-        var type = Type.GetType(name);
+        }
 
-        if (type != null)
+        string name = param.GetType().FullName!.Replace("ViewModel", "View", StringComparison.Ordinal);
+        Type? type = Type.GetType(name);
+        if (type is not null)
         {
             return (Control)Activator.CreateInstance(type)!;
         }
-        
-        return new TextBlock { Text = "Not Found: " + name };
+
+        return new TextBlock { Text = string.Format(YKanBan.Resources.Culture, YKanBan.Resources.Error_ViewNotFound, name) };
     }
 
-    public bool Match(object? data)
-    {
-        return data is ViewModelBase;
-    }
+    /// <inheritdoc/>
+    public bool Match(object? data) => data is ViewModelBase;
 }