refactor(claude-do): refactor(worker): move the merge and worktree MCP tools out

`src/ClaudeDo.Worker/External/ExternalMcpService.cs` ist **1897 Zeilen** (nachgezählt 2026-09-02; die Datei ist seit dem Anlegen dieses Tasks von 1696 weiter gewachsen): ~30 DTO-Records oben plus ~25 Tool-Methoden — während **13** Geschwisterdateien `*McpTools.cs` im selben Ordner das Topic-Split-Muster schon tragen (`ListMcpTools`, `ConfigMcpTools`, `BatchMcpTools`, `NotesMcpTools`, `QueueStateMc

ClaudeDo-Task: 1862e160-ffde-4a50-aa03-bb7251f56088

tests/ClaudeDo.Worker.Tests/External/BatchMcpToolsTests.cs

@@ -79,7 +79,6 @@ public sealed class BatchMcpToolsTests : IDisposable
     {
         var git = new GitService();
         var factory = _db.CreateFactory();
-        var maintenance = new WorktreeMaintenanceService(factory, git, NullLogger<WorktreeMaintenanceService>.Instance);
         var state = TaskStateServiceBuilder.Build(factory).State;
         var merge = new TaskMergeService(factory, git, _broadcaster, state, new VerifyCommandRunner(), NullLogger<TaskMergeService>.Instance);
         var aggregator = new PlanningAggregator(factory, git, NullLogger<PlanningAggregator>.Instance);
@@ -88,7 +87,7 @@ public sealed class BatchMcpToolsTests : IDisposable
         var svc = new ExternalMcpService(
             _tasks, _lists, CreateQueue(), _broadcaster,
             state,
-            git, factory, maintenance, merge, planningMerge,
+            git, factory, merge, planningMerge,
             new BaseDirtyChecker(git, NullLogger<BaseDirtyChecker>.Instance));
         return new BatchMcpTools(svc);
     }