Replace broadcastSceneNow() with incremental element:update for all
property-modifying operations (align, arrange, flip, resize, rotate,
normalize, frame color). Full scene sync now only fires via debounced
fallback (500ms) for structural changes (add/remove/paste/group).
Changes:
- onCanvasChange() accepts optional changedIds for incremental sync
- SelectionToolbar, context menu, shortcuts all pass item IDs
- TransformBox.onDragEnd passes item IDs instead of full scene
- ShortcutContext, MenuContext, hook interfaces updated
This dramatically reduces sync traffic during normal editing — only
the changed elements are sent instead of the entire board state.
Hiren Kangad
21ee4b2601