When a custom widget is added to a board in edit mode, the item only
exists in local TanStack cache (persisted on saveBoard at edit-mode
exit). The getData query fired immediately, hit the DB before the item
existed, threw NOT_FOUND, and retry was disabled so the widget stayed
on 'definition not found' until reload.
- Gate getData with !isEditMode so it only fires for persisted items
- Show an edit-mode placeholder instead of an empty box
- Add e2e regression test verifying no 'not found' before reload