fix(sticky): fixed-size creation, shared presets module, live resize sync

Fixes three review findings:

1. Sticky creation no longer zoom-adapts — always creates at M preset
   (28px/260w) in world space. Consistent at any zoom level.

2. Preset definitions extracted to stickyPresets.ts (shared domain module).
   TextFormatToolbar and tools.ts both import from there — no more
   canvas→component dependency inversion.

3. TextEditor.onLiveResize callback syncs spatial index and transform
   box as sticky background grows during typing.

frontend/src/pages/Editor.tsx

@@ -20,7 +20,8 @@ import UserCursors from '../components/UserCursors';
 import ContextMenu from '../components/ContextMenu';
 import LayerPanel from '../components/LayerPanel';
 import SelectionToolbar from '../components/SelectionToolbar';
-import TextFormatToolbar, { getStickyWidthForSize } from '../components/TextFormatToolbar';
+import TextFormatToolbar from '../components/TextFormatToolbar';
+import { getStickyWidthForSize } from '../canvas/stickyPresets';
 import VideoControls from '../components/VideoControls';
 import ShortcutsHelp from '../components/ShortcutsHelp';
 import MattermostImport from '../components/MattermostImport';