feat(m1): storage layer

- Shared SQLite plumbing: PRAGMAs (WAL/NORMAL/foreign_keys) and
  user_version migrations with typed SchemaVersionException
- Workspace folder: .ykanban initialization, empty schema with
  DDL-level constraints, preset column seeding (ResX-driven),
  exclusive lock file with holder diagnostics
- AppData folder: app.db workspace registry (injectable clock),
  app.json config store with kebab-case JSON names via explicit
  [JsonProperty]/[EnumMember], nested sections, corrupt-file backup
- ResX infrastructure under Assets/Locales (en + zh-Hans) with
  MSBuild strongly-typed public Resources class
- 54 unit tests: DDL constraints, migrations, PRAGMAs, lock
  exclusivity, config degradation, culture-aware presets

YKanBan.Tests/Storage/AppData/AppDatabaseTests.cs

@@ -0,0 +1,136 @@
+using Microsoft.Data.Sqlite;
+using YKanBan.Storage;
+using YKanBan.Storage.AppData;
+using YKanBan.Tests.TestUtilities;
+
+namespace YKanBan.Tests.Storage.AppData;
+
+/// <summary>Tests for the global app.db workspace registry.</summary>
+[TestClass]
+public class AppDatabaseTests
+{
+    private static string DatabasePath(TempDirectory directory)
+        => Path.Combine(directory.FullPath, "app.db");
+
+    [TestMethod]
+    public void UpsertInsertsRowWithTimestamps()
+    {
+        using var directory = new TempDirectory();
+        long now = 1000;
+        using var db = new AppDatabase(DatabasePath(directory), () => now);
+
+        db.UpsertWorkspace(@"C:\work\repo");
+
+        IReadOnlyList<WorkspaceRecord> records = db.GetWorkspaces();
+        Assert.AreEqual(1, records.Count);
+        Assert.AreEqual(@"C:\work\repo", records[0].Path);
+        Assert.AreEqual(1000L, records[0].AddedAt);
+        Assert.AreEqual(1000L, records[0].LastEditedAt);
+    }
+
+    [TestMethod]
+    public void RepeatedUpsertKeepsOriginalAddedAt()
+    {
+        using var directory = new TempDirectory();
+        long now = 1000;
+        using var db = new AppDatabase(DatabasePath(directory), () => now);
+
+        db.UpsertWorkspace(@"C:\work\repo");
+        now = 2000;
+        db.UpsertWorkspace(@"C:\work\repo");
+
+        WorkspaceRecord record = db.GetWorkspaces().Single();
+        Assert.AreEqual(1000L, record.AddedAt);
+        Assert.AreEqual(2000L, record.LastEditedAt);
+    }
+
+    [TestMethod]
+    public void TouchRefreshesLastEditedAt()
+    {
+        using var directory = new TempDirectory();
+        long now = 1000;
+        using var db = new AppDatabase(DatabasePath(directory), () => now);
+
+        db.UpsertWorkspace(@"C:\work\repo");
+        now = 2500;
+        db.TouchLastEdited(@"C:\work\repo");
+
+        WorkspaceRecord record = db.GetWorkspaces().Single();
+        Assert.AreEqual(1000L, record.AddedAt);
+        Assert.AreEqual(2500L, record.LastEditedAt);
+    }
+
+    [TestMethod]
+    public void TouchOnUnknownPathRegistersTheWorkspace()
+    {
+        using var directory = new TempDirectory();
+        long now = 3000;
+        using var db = new AppDatabase(DatabasePath(directory), () => now);
+
+        // Self-healing: touching an unregistered workspace still leaves a valid row.
+        db.TouchLastEdited(@"C:\work\other");
+
+        WorkspaceRecord record = db.GetWorkspaces().Single();
+        Assert.AreEqual(3000L, record.AddedAt);
+        Assert.AreEqual(3000L, record.LastEditedAt);
+    }
+
+    [TestMethod]
+    public void RemoveDeletesTheRow()
+    {
+        using var directory = new TempDirectory();
+        using var db = new AppDatabase(DatabasePath(directory));
+
+        db.UpsertWorkspace(@"C:\work\repo");
+        db.RemoveWorkspace(@"C:\work\repo");
+
+        Assert.AreEqual(0, db.GetWorkspaces().Count);
+    }
+
+    [TestMethod]
+    public void RowsPersistAcrossReopen()
+    {
+        using var directory = new TempDirectory();
+        string path = DatabasePath(directory);
+
+        using (var db = new AppDatabase(path, () => 1000))
+        {
+            db.UpsertWorkspace(@"C:\work\repo");
+        }
+
+        using var reopened = new AppDatabase(path, () => 9999);
+        WorkspaceRecord record = reopened.GetWorkspaces().Single();
+        Assert.AreEqual(@"C:\work\repo", record.Path);
+        Assert.AreEqual(1000L, record.AddedAt);
+    }
+
+    [TestMethod]
+    public void OpenMigratesToCurrentSchemaVersion()
+    {
+        using var directory = new TempDirectory();
+        string path = DatabasePath(directory);
+        using (var db = new AppDatabase(path))
+        {
+        }
+
+        using var raw = new SqliteConnection($"Data Source={path}");
+        raw.Open();
+        Assert.AreEqual(AppDatabase.CurrentSchemaVersion, SqliteDatabase.ReadUserVersion(raw));
+    }
+
+    [TestMethod]
+    public void OpenAppliesWalJournalMode()
+    {
+        using var directory = new TempDirectory();
+        string path = DatabasePath(directory);
+        using (var db = new AppDatabase(path))
+        {
+        }
+
+        // WAL is a persistent property of the database file: a plain new
+        // connection reports it without any PRAGMA replay.
+        using var raw = new SqliteConnection($"Data Source={path}");
+        raw.Open();
+        Assert.AreEqual("wal", SqliteTestHelper.ScalarString(raw, "PRAGMA journal_mode;"));
+    }
+}