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/Runner/LogWriter.cs

@@ -0,0 +1,26 @@
+namespace ClaudeDo.Worker.Runner;
+
+public sealed class LogWriter : IAsyncDisposable
+{
+    private readonly StreamWriter _writer;
+
+    public LogWriter(string filePath)
+    {
+        var dir = Path.GetDirectoryName(filePath);
+        if (dir is not null)
+            Directory.CreateDirectory(dir);
+
+        _writer = new StreamWriter(filePath, append: true) { AutoFlush = true };
+    }
+
+    public async Task WriteLineAsync(string line, CancellationToken ct = default)
+    {
+        ct.ThrowIfCancellationRequested();
+        await _writer.WriteLineAsync(line.AsMemory(), ct);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await _writer.DisposeAsync();
+    }
+}