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>

tests/ClaudeDo.Worker.Tests/Hub/AgentSettingsHubTests.cs

@@ -57,7 +57,7 @@ public sealed class AgentSettingsHubTests : IDisposable
             Directory.CreateDirectory(targetDir);
             await File.WriteAllTextAsync(Path.Combine(bundleDir, "code-reviewer.md"), "body");
 
-            var seeder = new ClaudeDo.Worker.Services.DefaultAgentSeeder(bundleDir, targetDir);
+            var seeder = new ClaudeDo.Worker.Agents.DefaultAgentSeeder(bundleDir, targetDir);
             var result = await seeder.SeedMissingAsync();
 
             Assert.Equal(1, result.Copied);

tests/ClaudeDo.Worker.Tests/Hub/PlanningHubTests.cs

@@ -4,8 +4,11 @@ using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Config;
 using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Agents;
+using ClaudeDo.Worker.Lifecycle;
 using ClaudeDo.Worker.Planning;
-using ClaudeDo.Worker.Services;
+using ClaudeDo.Worker.Queue;
+using ClaudeDo.Worker.Worktrees;
 using ClaudeDo.Worker.Tests.Infrastructure;
 using Microsoft.AspNetCore.SignalR;
 using Xunit;