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/Workspace/WorkspacePresetTests.cs

@@ -0,0 +1,39 @@
+using YKanBan.Storage.Workspace;
+using YKanBan.Tests.TestUtilities;
+
+namespace YKanBan.Tests.Storage.Workspace;
+
+/// <summary>Tests for seeding preset workspace content.</summary>
+[TestClass]
+public class WorkspacePresetTests
+{
+    [TestMethod]
+    public void SeedAddsThreeDistinctPresetColumns()
+    {
+        using var directory = new TempDirectory();
+        WorkspaceInitializer.Initialize(directory.FullPath);
+        WorkspacePreset.SeedColumns(directory.FullPath);
+
+        using var connection = SqliteTestHelper.OpenWorkspace(directory.FullPath);
+        List<string> titles = SqliteTestHelper.GetColumnTitles(connection);
+
+        Assert.AreEqual(3, titles.Count);
+        Assert.AreEqual(titles.Count, titles.Distinct().Count());
+        Assert.IsTrue(titles.All(title => title.Length > 0));
+    }
+
+    [TestMethod]
+    public void SeedPresetColumnsShareOneTimestamp()
+    {
+        using var directory = new TempDirectory();
+        WorkspaceInitializer.Initialize(directory.FullPath);
+        WorkspacePreset.SeedColumns(directory.FullPath);
+
+        using var connection = SqliteTestHelper.OpenWorkspace(directory.FullPath);
+
+        // Creation writes created_at = updated_at; all three columns share one moment.
+        Assert.AreEqual(0L, SqliteTestHelper.ScalarLong(connection, "SELECT COUNT(*) FROM columns WHERE created_at <> updated_at;"));
+        Assert.AreEqual(3L, SqliteTestHelper.ScalarLong(connection, "SELECT COUNT(*) FROM columns WHERE created_at > 0;"));
+        Assert.AreEqual(1L, SqliteTestHelper.ScalarLong(connection, "SELECT COUNT(DISTINCT created_at) FROM columns;"));
+    }
+}