feat(worker): batch MCP tools for the external endpoint

Add seven best-effort batch variants of the single-entity external MCP
tools: batch_get_tasks, batch_add_tasks, batch_update_task_status,
batch_cancel_tasks, batch_delete_tasks, batch_set_my_day, and
batch_cleanup_task_worktrees. Each loops the existing ExternalMcpService
methods sequentially (scoped DbContext is not thread-safe), returns a
per-item result array so a failing item never aborts the rest, and
rejects empty or over-100-item batches. Merge/review stay single-task.

src/ClaudeDo.Worker/Program.cs

@@ -264,6 +264,7 @@ if (cfg.ExternalMcpPort > 0)
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<WorktreeMaintenanceService>());
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<TaskMergeService>());
     externalBuilder.Services.AddScoped<ExternalMcpService>();
+    externalBuilder.Services.AddScoped<BatchMcpTools>();
     externalBuilder.Services.AddScoped<ListMcpTools>();
     externalBuilder.Services.AddScoped<ConfigMcpTools>();
     externalBuilder.Services.AddScoped<RunHistoryMcpTools>();
@@ -276,6 +277,7 @@ if (cfg.ExternalMcpPort > 0)
     externalBuilder.Services.AddMcpServer()
         .WithHttpTransport()
         .WithTools<ExternalMcpService>()
+        .WithTools<BatchMcpTools>()
         .WithTools<ListMcpTools>()
         .WithTools<ConfigMcpTools>()
         .WithTools<RunHistoryMcpTools>()