fix: restore erase sweep on right-click-drag

Right-click on note = delete. Right-click + drag on empty space =
erase sweep. Resets on mouseup so brush works after menu closes.

app/static/js/app.jsx

@@ -4912,7 +4912,7 @@ const PianoRollTabEditor = ({ st, zoom, bpm, viewportWidth, onClose, onUpdateNot
 
     if (scaleMenuPos) setScaleMenuPos(null);
 
-    // Right click -> Quick delete note
+    // Right click -> delete note or start erase sweep (drag to sweep)
     if (e.button === 2) {
       e.preventDefault();
       const clickedNote = notes.find(n => {
@@ -4923,6 +4923,9 @@ const PianoRollTabEditor = ({ st, zoom, bpm, viewportWidth, onClose, onUpdateNot
         setNotes(prev => prev.filter(n => n.id !== clickedNote.id));
         setSelectedNoteIds(prev => prev.filter(id => id !== clickedNote.id));
         showToast('Đã xóa nốt!', 'info');
+      } else {
+        notesBeforeDragRef.current = JSON.parse(JSON.stringify(notes));
+        setDraggedNote({ mode: 'erase_sweep', visitedPitches: [pitch] });
       }
       return;
     }