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/Hub/WorkerHub.cs

@@ -3,6 +3,7 @@ using ClaudeDo.Data;
 using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Planning;
+using ClaudeDo.Worker.Queue;
 using ClaudeDo.Worker.Services;
 using Microsoft.AspNetCore.SignalR;
 using Microsoft.EntityFrameworkCore;
@@ -37,6 +38,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         Assembly.GetExecutingAssembly().GetName().Version?.ToString(3) ?? "0.0.0";
 
     private readonly QueueService _queue;
+    private readonly IQueueWaker _waker;
     private readonly AgentFileService _agentService;
     private readonly DefaultAgentSeeder _seeder;
     private readonly HubBroadcaster _broadcaster;
@@ -52,6 +54,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
 
     public WorkerHub(
         QueueService queue,
+        IQueueWaker waker,
         AgentFileService agentService,
         DefaultAgentSeeder seeder,
         HubBroadcaster broadcaster,
@@ -66,6 +69,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         PlanningChainCoordinator planningChain)
     {
         _queue = queue;
+        _waker = waker;
         _agentService = agentService;
         _seeder = seeder;
         _broadcaster = broadcaster;
@@ -99,8 +103,6 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         await _broadcaster.TaskUpdated(parentTaskId);
         foreach (var id in childIds)
             await _broadcaster.TaskUpdated(id);
-
-        _queue.WakeQueue();
     }
 
     public string Ping() => $"pong v{Version}";
@@ -162,7 +164,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
 
     public bool CancelTask(string taskId) => _queue.CancelTask(taskId);
 
-    public void WakeQueue() => _queue.WakeQueue();
+    public void WakeQueue() => _waker.Wake();
 
     public async Task<List<AgentInfo>> GetAgents() => await _agentService.ScanAsync();