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.Ui.Tests/ViewModels/MissionControlViewModelTests.cs

@@ -228,14 +228,15 @@ public class MissionControlViewModelTests : IDisposable
 
         public QueueingWorkerClient(Func<ClaudeDoDbContext> newContext) => _newContext = newContext;
 
-        public override async Task SetTaskStatusAsync(string taskId, TaskStatus status)
+        public override async Task<BaseDirtyWarningDto?> SetTaskStatusAsync(string taskId, TaskStatus status)
         {
             QueuedTaskIds.Add(taskId);
             await using var db = _newContext();
             var entity = await db.Tasks.FirstOrDefaultAsync(t => t.Id == taskId);
-            if (entity is null) return;
+            if (entity is null) return null;
             entity.Status = status;
             await db.SaveChangesAsync();
+            return null;
         }
     }