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/ViewModels/TaskEditorViewModel.cs

@@ -113,6 +113,11 @@ public partial class TaskEditorViewModel : ViewModelBase
         RequestClose?.Invoke();
     }
 
+    public void OnWindowClosed()
+    {
+        _tcs.TrySetResult(null);
+    }
+
     public Task<TaskEntity?> ShowAndWaitAsync()
     {
         _tcs = new TaskCompletionSource<TaskEntity?>();