refactor(worker/queue): split queue waker and picker, auto-wake on enqueue

Slice 3 of the worker state and queue consolidation refactor.

- Add IQueueWaker / QueueWaker (singleton holding the wake semaphore).
- Add IQueuePicker / QueuePicker; raw SQL UPDATE...RETURNING moves out of
  TaskRepository.GetNextQueuedAgentTaskAsync (deleted) and now also filters
  on blocked_by_task_id IS NULL and writes started_at on claim.
- TaskStateService takes IQueueWaker directly; the Func<QueueService>
  indirection is gone. State transitions to Queued auto-wake the dispatcher.
- QueueService waits via the shared waker and dispatches via the picker.
- Drop explicit _queue.WakeQueue() calls in WorkerHub.QueuePlanningSubtasksAsync
  and ExternalMcpService.AddTask. The hub WakeQueue endpoint stays for
  diagnostics, delegating to _waker.Wake().
- Migrate tests; pre-existing flaky AppSettings/ExternalMcp tests untouched.

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

src/ClaudeDo.Worker/State/TaskStateService.cs

@@ -3,6 +3,7 @@ using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Hub;
 using ClaudeDo.Worker.Planning;
+using ClaudeDo.Worker.Queue;
 using Microsoft.EntityFrameworkCore;
 using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
@@ -12,20 +13,20 @@ public sealed class TaskStateService : ITaskStateService
 {
     private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
     private readonly HubBroadcaster _broadcaster;
-    private readonly Action _wakeQueue;
+    private readonly IQueueWaker _waker;
     private readonly PlanningChainCoordinator _chain;
     private readonly ILogger<TaskStateService> _logger;
 
     public TaskStateService(
         IDbContextFactory<ClaudeDoDbContext> dbFactory,
         HubBroadcaster broadcaster,
-        Action wakeQueue,
+        IQueueWaker waker,
         PlanningChainCoordinator chain,
         ILogger<TaskStateService> logger)
     {
         _dbFactory = dbFactory;
         _broadcaster = broadcaster;
-        _wakeQueue = wakeQueue;
+        _waker = waker;
         _chain = chain;
         _logger = logger;
     }
@@ -40,7 +41,7 @@ public sealed class TaskStateService : ITaskStateService
         if (affected == 0)
             return new TransitionResult(false, "Task not found or already running.");
 
-        _wakeQueue();
+        _waker.Wake();
         await _broadcaster.TaskUpdated(taskId);
         return new TransitionResult(true, null);
     }
@@ -203,7 +204,7 @@ public sealed class TaskStateService : ITaskStateService
             .Where(t => t.Id == taskId && t.Status == TaskStatus.Waiting)
             .ExecuteUpdateAsync(s => s.SetProperty(t => t.Status, TaskStatus.Queued), ct);
 
-        _wakeQueue();
+        _waker.Wake();
         await _broadcaster.TaskUpdated(taskId);
         return new TransitionResult(true, null);
     }