refactor(worker): extract OverrideSlotService and reorganize Worker/Services into domain folders

Slice 5 of the worker state consolidation refactor.

OverrideSlotService (new in Worker/Queue/) owns RunNow, ContinueTask,
and the override-slot piece of CancelTask. QueueService keeps the
queue-slot guard for "task is already running" rejection and delegates
to OverrideSlotService for execution; CancelTask tries the override
slot first, then the queue slot. QueueSlotState is extracted to its own
file.

Folder reorg (via git mv to preserve history):
- Worker/Queue/      QueueService, OverrideSlotService, QueueSlotState
                     (alongside existing waker/picker)
- Worker/Lifecycle/  StaleTaskRecovery, TaskResetService, TaskMergeService
- Worker/Worktrees/  WorktreeMaintenanceService
- Worker/Agents/     AgentFileService, DefaultAgentSeeder

Worker/Services/ folder removed. All consumers updated to the new
namespaces (Program.cs, WorkerHub, ExternalMcpService,
PlanningMergeOrchestrator, all Worker tests).

OverrideSlotService is registered as a DI singleton in both the main
worker app and the external MCP app.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Worker/Queue/OverrideSlotService.cs

@@ -0,0 +1,134 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Runner;
+using Microsoft.EntityFrameworkCore;
+
+namespace ClaudeDo.Worker.Queue;
+
+public sealed class OverrideSlotService
+{
+    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+    private readonly TaskRunner _runner;
+    private readonly ILogger<OverrideSlotService> _logger;
+
+    private readonly object _lock = new();
+    private volatile QueueSlotState? _slot;
+
+    public OverrideSlotService(
+        IDbContextFactory<ClaudeDoDbContext> dbFactory,
+        TaskRunner runner,
+        ILogger<OverrideSlotService> logger)
+    {
+        _dbFactory = dbFactory;
+        _runner = runner;
+        _logger = logger;
+    }
+
+    public QueueSlotState? CurrentSlot => _slot;
+
+    public async Task RunNow(string taskId)
+    {
+        using (var context = _dbFactory.CreateDbContext())
+        {
+            var taskRepo = new TaskRepository(context);
+            var exists = await taskRepo.GetByIdAsync(taskId);
+            if (exists is null)
+                throw new KeyNotFoundException($"Task '{taskId}' not found.");
+        }
+
+        lock (_lock)
+        {
+            if (_slot is not null)
+                throw new InvalidOperationException("override slot busy");
+
+            var cts = new CancellationTokenSource();
+            _slot = new QueueSlotState { TaskId = taskId, StartedAt = DateTime.UtcNow, Cts = cts };
+
+            _ = RunInSlotAsync(taskId, cts.Token).ContinueWith(t =>
+            {
+                if (t.IsFaulted)
+                    _logger.LogError(t.Exception, "RunInSlotAsync failed for task {TaskId}", taskId);
+                lock (_lock) { _slot = null; }
+                cts.Dispose();
+            }, TaskScheduler.Default);
+        }
+    }
+
+    public async Task<string> ContinueTask(string taskId, string followUpPrompt)
+    {
+        using var context = _dbFactory.CreateDbContext();
+        var taskRepo = new TaskRepository(context);
+        var task = await taskRepo.GetByIdAsync(taskId)
+            ?? throw new KeyNotFoundException($"Task '{taskId}' not found.");
+
+        if (task.Status == Data.Models.TaskStatus.Running)
+            throw new InvalidOperationException("task is already running");
+
+        lock (_lock)
+        {
+            if (_slot is not null)
+                throw new InvalidOperationException("override slot busy");
+
+            var cts = new CancellationTokenSource();
+            _slot = new QueueSlotState { TaskId = taskId, StartedAt = DateTime.UtcNow, Cts = cts };
+
+            _ = RunContinueInSlotAsync(taskId, followUpPrompt, cts.Token).ContinueWith(t =>
+            {
+                if (t.IsFaulted)
+                    _logger.LogError(t.Exception, "RunContinueInSlotAsync failed for task {TaskId}", taskId);
+                lock (_lock) { _slot = null; }
+                cts.Dispose();
+            }, TaskScheduler.Default);
+        }
+
+        return taskId;
+    }
+
+    public bool TryCancel(string taskId)
+    {
+        lock (_lock)
+        {
+            if (_slot is not null && _slot.TaskId == taskId)
+            {
+                _slot.Cts.Cancel();
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private async Task RunInSlotAsync(string taskId, CancellationToken ct)
+    {
+        try
+        {
+            _logger.LogInformation("Starting task {TaskId} in override slot", taskId);
+
+            Data.Models.TaskEntity task;
+            using (var context = _dbFactory.CreateDbContext())
+            {
+                var taskRepo = new TaskRepository(context);
+                task = await taskRepo.GetByIdAsync(taskId, ct)
+                    ?? throw new KeyNotFoundException($"Task '{taskId}' not found.");
+            }
+
+            await _runner.RunAsync(task, "override", ct);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Override slot runner error for task {TaskId}", taskId);
+        }
+    }
+
+    private async Task RunContinueInSlotAsync(string taskId, string followUpPrompt, CancellationToken ct)
+    {
+        try
+        {
+            _logger.LogInformation("Continuing task {TaskId} in override slot", taskId);
+            await _runner.ContinueAsync(taskId, followUpPrompt, "override", ct);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Continue runner error for task {TaskId}", taskId);
+        }
+    }
+}