fix(ui): surface worker-offline failures when deleting a task

DeleteTaskAsync had no IsConnected guard, unlike every other worker-dependent
command in DetailsIslandViewModel, so an offline delete was a silent no-op.
WorkerClient.DeleteTaskAsync also only caught HubException, letting the
InvalidOperationException thrown by an inactive hub connection escape into
the unobserved command task and vanish.

Gate DeleteTaskCommand behind CanDeleteTask (Task != null && IsConnected),
re-evaluate it on connection-state changes, widen WorkerClient to catch the
connection-inactive case too, and wrap the ViewModel's call in try/catch as
a second line of defense against a race between the guard and the call.

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

@@ -355,6 +355,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
                 ContinueCommand.NotifyCanExecuteChanged();
                 SendRoadblockReplyCommand.NotifyCanExecuteChanged();
                 CancelReviewCommand.NotifyCanExecuteChanged();
+                DeleteTaskCommand.NotifyCanExecuteChanged();
             }
         };
         _worker.PropertyChanged += _workerPropertyChangedHandler;
@@ -963,7 +964,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
         await repo.UpdateAsync(entity);
     }
 
-    [RelayCommand]
+    [RelayCommand(CanExecute = nameof(CanDeleteTask))]
     private async System.Threading.Tasks.Task DeleteTaskAsync()
     {
         if (Task == null) return;
@@ -976,7 +977,20 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
         // Routed through the worker (mirrors the MCP delete_task tool) so a deleted child
         // correctly advances a WaitingForChildren parent — a direct-repo delete from here used
         // to bypass TaskStateService.TryAdvanceParentAsync and could wedge the parent forever.
-        var (deleted, error) = await _worker.DeleteTaskAsync(row.Id);
+        bool deleted;
+        string? error;
+        try
+        {
+            (deleted, error) = await _worker.DeleteTaskAsync(row.Id);
+        }
+        catch (Exception ex)
+        {
+            // Belt and braces: the connection can drop between the CanExecute check and
+            // this call, so a stray throw here must surface, not vanish silently.
+            if (ShowErrorAsync != null)
+                await ShowErrorAsync(ex.Message);
+            return;
+        }
         if (!deleted)
         {
             if (ShowErrorAsync != null)
@@ -988,6 +1002,8 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
         CloseDetail?.Invoke();
     }
 
+    private bool CanDeleteTask() => Task != null && _worker.IsConnected;
+
     [RelayCommand]
     private async System.Threading.Tasks.Task CommitSubtaskEditAsync(SubtaskRowViewModel? row)
     {