feat(data,worker): add repositories, stale-task recovery, and test foundation

Data: TagRepository, ListRepository, TaskRepository (incl. queue selection via
effective agent tag + scheduled_for filter), WorktreeRepository. All CRUD via
parameterized SqliteCommand; enums roundtrip as lowercase strings matching the
schema CHECK constraints.

Worker: StaleTaskRecovery IHostedService flips running -> failed on startup and
marks the result column with a [stale] reason. All four repositories registered
as singletons.

Tests: DbFixture with temp-file SQLite + schema bootstrap, covering
TaskRepository (queue pick via list-tag and task-tag, schedule filter,
transitions, stale flip), ListRepository CRUD + junctions, and
StaleTaskRecovery. 14 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/ClaudeDo.Worker.Tests/Infrastructure/DbFixture.cs

@@ -0,0 +1,23 @@
+using ClaudeDo.Data;
+
+namespace ClaudeDo.Worker.Tests.Infrastructure;
+
+public sealed class DbFixture : IDisposable
+{
+    public string DbPath { get; }
+    public SqliteConnectionFactory Factory { get; }
+
+    public DbFixture()
+    {
+        DbPath = Path.Combine(Path.GetTempPath(), $"claudedo_test_{Guid.NewGuid():N}.db");
+        Factory = new SqliteConnectionFactory(DbPath);
+        SchemaInitializer.Apply(Factory);
+    }
+
+    public void Dispose()
+    {
+        try { File.Delete(DbPath); } catch { /* best effort */ }
+        try { File.Delete(DbPath + "-wal"); } catch { }
+        try { File.Delete(DbPath + "-shm"); } catch { }
+    }
+}