fix(ui): fix live output visibility and editor dialog graying out

- Remove wrapping ScrollViewer from live output TextBox — Avalonia
  TextBox with AcceptsReturn handles its own scrolling; nested
  ScrollViewer caused layout collapse
- Auto-scroll via CaretIndex instead of removed ScrollViewer
- Add OnWindowClosed to both editor ViewModels, ensuring the
  TaskCompletionSource always resolves when the dialog closes
  (including via X button), preventing RelayCommand from staying
  permanently disabled

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Ui/Views/TaskDetailView.axaml.cs

@@ -49,8 +49,11 @@ public partial class TaskDetailView : UserControl
     {
         if (e.PropertyName == nameof(TaskDetailViewModel.LiveText))
         {
-            var scroll = this.FindControl<ScrollViewer>("LiveOutputScroll");
-            scroll?.ScrollToEnd();
+            var box = this.FindControl<TextBox>("LiveOutputBox");
+            if (box is not null)
+            {
+                box.CaretIndex = box.Text?.Length ?? 0;
+            }
         }
     }
 }