feat(worker): add claude-cli runner, queue service, and hub api

Runner stack (non-worktree path): IClaudeProcess + ClaudeProcess spawning the
CLI with --output-format stream-json, prompt via stdin, parses the final
type:"result" line into RunResult. LogWriter appends ndjson to
~/.todo-app/logs/<taskId>.ndjson. TaskRunner orchestrates DB transitions
(MarkRunning -> MarkDone/Failed) and pushes TaskStarted/Message/Finished/
Updated via HubBroadcaster. Worktree-backed lists short-circuit with a
"Slice E" failure message until git support lands.

QueueService (BackgroundService) holds two in-memory slots (_queueSlot +
_overrideSlot) guarded by a lock. Uses PeriodicTimer + SemaphoreSlim wake
signal so WakeQueue() triggers an instant pickup. RunNow throws
InvalidOperationException when override busy; CancelTask cancels the linked
CTS which kills the child process tree.

WorkerHub extended with GetActive, RunNow (translated to HubException
variants), CancelTask, WakeQueue. HubBroadcaster exposes typed push methods.

Tests: 26 pass (12 new). QueueServiceTests cover override-busy,
schedule-filter, FIFO sequentiality, cancellation, plus a FakeClaudeProcess
that blocks on a TCS for deterministic slot-state assertions.
MessageParserTests cover result extraction + malformed/non-result lines.

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

src/ClaudeDo.Worker/Hub/HubBroadcaster.cs

@@ -0,0 +1,25 @@
+using Microsoft.AspNetCore.SignalR;
+
+namespace ClaudeDo.Worker.Hub;
+
+public sealed class HubBroadcaster
+{
+    private readonly IHubContext<WorkerHub> _hub;
+
+    public HubBroadcaster(IHubContext<WorkerHub> hub) => _hub = hub;
+
+    public Task TaskStarted(string slot, string taskId, DateTime startedAt) =>
+        _hub.Clients.All.SendAsync("TaskStarted", slot, taskId, startedAt);
+
+    public Task TaskFinished(string slot, string taskId, string status, DateTime finishedAt) =>
+        _hub.Clients.All.SendAsync("TaskFinished", slot, taskId, status, finishedAt);
+
+    public Task TaskMessage(string taskId, string ndjsonLine) =>
+        _hub.Clients.All.SendAsync("TaskMessage", taskId, ndjsonLine);
+
+    public Task WorktreeUpdated(string taskId) =>
+        _hub.Clients.All.SendAsync("WorktreeUpdated", taskId);
+
+    public Task TaskUpdated(string taskId) =>
+        _hub.Clients.All.SendAsync("TaskUpdated", taskId);
+}