Fix TUI redraw after event-driven updates (#196)

## Summary
- flush the live view when the UI refresh loop wakes up from an
event-driven refresh request

## Testing
- ./scripts/run-in-env.sh pytest tests/tui/test_volume_state.py
- ./scripts/run-in-env.sh ruff check sendspin/tui/ui.py

Author: balloob

sendspin/tui/ui.py

@@ -203,6 +203,7 @@ async def _refresh_loop(self) -> None:
                 break
             else:
                 event.clear()
+                self._flush_refresh()
 
     def _shortcut_style(self, shortcut: str) -> str:
         """Get the style for a shortcut key."""