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>

tests/ClaudeDo.Worker.Tests/Runner/MessageParserTests.cs

@@ -0,0 +1,53 @@
+using ClaudeDo.Worker.Runner;
+
+namespace ClaudeDo.Worker.Tests.Runner;
+
+public sealed class MessageParserTests
+{
+    [Fact]
+    public void WellFormed_Result_Line_Extracts_Result()
+    {
+        var line = """{"type":"result","result":"Hello **world**"}""";
+        Assert.True(MessageParser.TryExtractResult(line, out var result));
+        Assert.Equal("Hello **world**", result);
+    }
+
+    [Fact]
+    public void Non_Result_Type_Returns_False()
+    {
+        var line = """{"type":"assistant","message":"hi"}""";
+        Assert.False(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Missing_Type_Property_Returns_False()
+    {
+        var line = """{"result":"data"}""";
+        Assert.False(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Malformed_Json_Returns_False_No_Throw()
+    {
+        var line = "this is not json {{{";
+        Assert.False(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Empty_Line_Returns_False()
+    {
+        Assert.False(MessageParser.TryExtractResult("", out _));
+        Assert.False(MessageParser.TryExtractResult("   ", out _));
+    }
+
+    [Fact]
+    public void Null_Result_Value_Returns_True_With_Null()
+    {
+        var line = """{"type":"result","result":null}""";
+        Assert.True(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+}