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>

tests/ClaudeDo.Worker.Tests/Repositories/TaskRepositoryPlanningTests.cs

@@ -302,28 +302,4 @@ public sealed class TaskRepositoryPlanningTests : IDisposable
         Assert.NotNull(stillThere);
     }
 
-    [Fact]
-    public async Task GetNextQueuedAgentTask_SkipsDraftPlanningPlanned()
-    {
-        var listId = await CreateListAsync();
-        var agentTagId = await _tags.GetOrCreateAsync("agent");
-
-        async Task<TaskEntity> T(TaskStatus s, bool withTag, string? parent = null)
-        {
-            var t = MakeTask(listId, s, parentId: parent);
-            await _tasks.AddAsync(t);
-            if (withTag) await _tasks.AddTagAsync(t.Id, agentTagId);
-            return t;
-        }
-
-        var planning = await T(TaskStatus.Planning, withTag: true);
-        var planned = await T(TaskStatus.Planned, withTag: true);
-        var draft = await T(TaskStatus.Draft, withTag: true, parent: planning.Id);
-        var queued = await T(TaskStatus.Queued, withTag: true);
-
-        var picked = await _tasks.GetNextQueuedAgentTaskAsync(DateTime.UtcNow);
-
-        Assert.NotNull(picked);
-        Assert.Equal(queued.Id, picked!.Id);
-    }
 }