feat(queue): warn when the base branch has uncommitted changes

Queuing (update_task_status, batch_update_task_status) and run_task_now
now surface a non-blocking baseDirty warning (separate modified/untracked
counts) when the list's working dir has uncommitted changes at enqueue
time, since a new worktree forks from the commit tip and silently misses
them. BaseDirtyChecker caches per working dir for a few seconds so a
batch queue over many tasks in one list only shells out to git once. The
UI surfaces the same warning via the footer error strip on queue actions.

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

@@ -4,6 +4,7 @@ using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Config;
 using ClaudeDo.Worker.External;
+using ClaudeDo.Worker.Git;
 using ClaudeDo.Worker.Hub;
 using ClaudeDo.Worker.Lifecycle;
 using ClaudeDo.Worker.Planning;
@@ -136,7 +137,8 @@ public sealed class ExternalMcpServiceTests : IDisposable
         return new ExternalMcpService(
             _tasks, _lists, queue, _broadcaster,
             state,
-            git, factory, maintenance, merge, planningMerge);
+            git, factory, maintenance, merge, planningMerge,
+            new BaseDirtyChecker(git, NullLogger<BaseDirtyChecker>.Instance));
     }
 
     private QueueService CreateQueue()