refactor(worker/state): introduce TaskStateService and route mutations through it

Slice 2 of the worker state consolidation refactor (spec sections 2 and 8).

Adds Worker/State/ITaskStateService + TaskStateService as the single component
that mutates Status, PlanningPhase, and BlockedByTaskId. Each transition is one
atomic ExecuteUpdate with a WHERE filter on the expected source status, so
parallel claims are TOCTOU-free. Side effects (queue wake on -> Queued, hub
TaskUpdated broadcast, chain advance + parent completion on terminal child)
are owned by the service so callers no longer need to remember them.

Migrated callers (mechanical, behavior preserved):
- TaskRunner: HandleSuccess/HandleFailure/MarkFailed/RunAsync/ContinueAsync
- StaleTaskRecovery: bulk recover stale Running tasks
- TaskResetService: status flip (worktree cleanup stays in service)
- PlanningSessionManager.StartAsync: status flip via state, token write via repo
- PlanningChainCoordinator.OnChildFinishedAsync: routes the next-sibling write
  through state.UnblockAsync (Slice 4 finishes the rewrite)
- ExternalMcpService.UpdateTaskStatus: Queued case via state.EnqueueAsync

Repo Mark*Async helpers (MarkRunning/MarkDone/MarkFailed/FlipAllRunningToFailed)
are now internal; ClaudeDo.Data grants InternalsVisibleTo to ClaudeDo.Worker
and ClaudeDo.Worker.Tests for the existing repo-level tests.

DI: TaskStateService is registered as Singleton in both the main app and the
external-MCP app; the queue-wake delegate captures sp -> QueueService.WakeQueue
to break the TaskStateService -> QueueService -> TaskRunner -> TaskStateService
construction cycle. PlanningChainCoordinator takes Func<ITaskStateService> for
the same reason; Slice 3 will replace both with IQueueWaker.

Tests: TaskStateServiceTests covers happy + reject for every transition, the
parallel StartRunningAsync claim race, child-terminal chain advancement, and
stale recovery. Existing service/repo tests are updated to construct the new
state-service via a TaskStateServiceBuilder helper. Pre-existing constructor
drift in QueueService/ExternalMcp/PlanningHub tests is patched to keep the
test project building (the surrounding test logic is otherwise untouched).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Data/Repositories/TaskRepository.cs

@@ -88,7 +88,7 @@ public sealed class TaskRepository
 
     #region Status transitions
 
-    public async Task MarkRunningAsync(string taskId, DateTime startedAt, CancellationToken ct = default)
+    internal async Task MarkRunningAsync(string taskId, DateTime startedAt, CancellationToken ct = default)
     {
         await _context.Tasks
             .Where(t => t.Id == taskId)
@@ -97,7 +97,7 @@ public sealed class TaskRepository
                 .SetProperty(t => t.StartedAt, startedAt), ct);
     }
 
-    public async Task MarkDoneAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
+    internal async Task MarkDoneAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
     {
         await _context.Tasks
             .Where(t => t.Id == taskId)
@@ -107,7 +107,7 @@ public sealed class TaskRepository
                 .SetProperty(t => t.Result, result), ct);
     }
 
-    public async Task MarkFailedAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
+    internal async Task MarkFailedAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
     {
         await _context.Tasks
             .Where(t => t.Id == taskId)
@@ -124,7 +124,7 @@ public sealed class TaskRepository
             .ExecuteUpdateAsync(s => s.SetProperty(t => t.LogPath, logPath), ct);
     }
 
-    public async Task<int> FlipAllRunningToFailedAsync(string reason, CancellationToken ct = default)
+    internal async Task<int> FlipAllRunningToFailedAsync(string reason, CancellationToken ct = default)
     {
         var resultText = "[stale] " + reason;
         var now = DateTime.UtcNow;
@@ -364,6 +364,17 @@ public sealed class TaskRepository
         return await _context.Tasks.AsNoTracking().FirstOrDefaultAsync(t => t.Id == taskId, ct);
     }
 
+    public async Task SetPlanningSessionTokenAsync(
+        string taskId,
+        string sessionToken,
+        CancellationToken ct = default)
+    {
+        await _context.Tasks
+            .Where(t => t.Id == taskId)
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(t => t.PlanningSessionToken, sessionToken), ct);
+    }
+
     public async Task UpdatePlanningSessionIdAsync(
         string parentId,
         string sessionId,