fix(ui): surface merge-drain cancel rejection in task-row quick cancel

TasksIslandViewModel.CancelReviewAsync swallowed the HubException the
worker raises when a task's unit merge is draining (79f90a9), unlike
the details-pane version fixed in the same commit. Mirror that fix:
report the rejection via ErrorReported instead of a bare catch.

src/ClaudeDo.Ui/ViewModels/Islands/TasksIslandViewModel.cs

@@ -930,7 +930,7 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
     {
         if (row is null || !row.IsWaitingForReview || _worker is null) return;
         try { await _worker.CancelReviewAsync(row.Id); }
-        catch { /* offline; broadcast reconciles on return */ }
+        catch (Exception ex) { ErrorReported?.Invoke(Loc.T("vm.tasksIsland.cancelReviewFailed", ex.Message)); }
     }
 
     public async Task SetScheduledForAsync(TaskRowViewModel row, DateTime? when)