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/WorkspaceInitializerTests.cs

@@ -0,0 +1,53 @@
+using YKanBan.Storage;
+using YKanBan.Storage.Workspace;
+using YKanBan.Tests.TestUtilities;
+
+namespace YKanBan.Tests.Storage.Workspace;
+
+/// <summary>Tests for .ykanban folder and empty database creation.</summary>
+[TestClass]
+public class WorkspaceInitializerTests
+{
+    [TestMethod]
+    public void InitializeCreatesYkanbanFolderAndDatabase()
+    {
+        using var directory = new TempDirectory();
+
+        Assert.IsFalse(WorkspaceInitializer.IsWorkspace(directory.FullPath));
+        WorkspaceInitializer.Initialize(directory.FullPath);
+
+        Assert.IsTrue(WorkspaceInitializer.IsWorkspace(directory.FullPath));
+        Assert.IsTrue(File.Exists(WorkspacePaths.Database(directory.FullPath)));
+        // The lock file only appears once a WorkspaceLock is acquired.
+        Assert.IsFalse(File.Exists(WorkspacePaths.LockFile(directory.FullPath)));
+    }
+
+    [TestMethod]
+    public void InitializeLeavesDatabaseEmpty()
+    {
+        // Initialization creates structure only; preset content is seeded separately.
+        using var directory = new TempDirectory();
+        WorkspaceInitializer.Initialize(directory.FullPath);
+
+        using var connection = SqliteTestHelper.OpenWorkspace(directory.FullPath);
+        Assert.AreEqual(0L, SqliteTestHelper.ScalarLong(connection, "SELECT COUNT(*) FROM columns;"));
+        Assert.AreEqual(0L, SqliteTestHelper.ScalarLong(connection, "SELECT COUNT(*) FROM cards;"));
+        Assert.AreEqual(0L, SqliteTestHelper.ScalarLong(connection, "SELECT COUNT(*) FROM tags;"));
+    }
+
+    [TestMethod]
+    public void InitializeThrowsWhenDirectoryIsMissing()
+    {
+        string missing = Path.Combine(Path.GetTempPath(), "ykanban-tests-" + Guid.NewGuid().ToString("N"));
+        Assert.ThrowsExactly<WorkspaceDirectoryMissingException>(() => WorkspaceInitializer.Initialize(missing));
+    }
+
+    [TestMethod]
+    public void InitializeThrowsWhenDatabaseAlreadyExists()
+    {
+        using var directory = new TempDirectory();
+        WorkspaceInitializer.Initialize(directory.FullPath);
+
+        Assert.ThrowsExactly<InvalidOperationException>(() => WorkspaceInitializer.Initialize(directory.FullPath));
+    }
+}