fix: address code review findings from crop/text commit

- CropOverlay: register move/up handlers dynamically on drag start (single
  handler instead of 8x per-handle), remove on drag end. Override destroy()
  to call _cleanup() preventing keyboard listener leaks.
- Text format toolbar: re-measure text bounds (w/h) after fontSize/fontFamily
  changes, update spatial index and transform box.
- TextEditor: add clearText() method; tools.ts uses it instead of fragile
  document.querySelector('textarea').
- SceneManager._updateItem: apply crop mask on remote sync for image items.
- useCanvasSetup: stop TextEditor on unmount to prevent orphaned textarea.
- Double-click zoom: use item.data dimensions instead of getBounds() (which
  includes shadow offset).

frontend/src/canvas/SceneManager.ts

@@ -421,6 +421,10 @@ export class SceneManager {
     if (data.type === 'group' && obj instanceof FrameSprite) {
       obj.updateFromData(data as GroupObject);
     }
+    if (data.type === 'image' && obj instanceof ImageSprite) {
+      const imgData = data as ImageObject;
+      obj.applyCrop(imgData.crop);
+    }
 
     // Update stored data
     item.data = { ...data };