perf(frontend): instant checkbox feedback via local optimistic selection in virtualized list

packages/frontend/src/components/PaginatedSongList.tsx

@@ -61,12 +61,18 @@ const SongItem = memo<{
 }>(({ song, isSelected, isHighlighted, onSelect, onToggleSelection, showCheckbox, onPlaySong, showDropIndicatorTop, onDragStart, onRowDragOver, onRowDrop, onRowDragStartCapture }) => {
   // Memoize the formatted duration to prevent recalculation
   const formattedDuration = useMemo(() => formatDuration(song.totalTime || ''), [song.totalTime]);
+  // Local optimistic selection for instant visual feedback
+  const [localChecked, setLocalChecked] = useState<boolean>(isSelected);
+  useEffect(() => {
+    setLocalChecked(isSelected);
+  }, [isSelected]);
   const handleClick = useCallback(() => {
     onSelect(song);
   }, [onSelect, song]);
 
   const handleCheckboxClick = useCallback((e: React.ChangeEvent<HTMLInputElement>) => {
     e.stopPropagation();
+    setLocalChecked(e.target.checked);
     onToggleSelection(song.id);
   }, [onToggleSelection, song.id]);
 
@@ -103,7 +109,7 @@ const SongItem = memo<{
       )}
       {showCheckbox && (
         <Checkbox
-          isChecked={isSelected}
+          isChecked={localChecked}
           onChange={handleCheckboxClick}
           mr={3}
           onClick={(e) => e.stopPropagation()}