useYjsPoiSync: Bidirectional sync between local POI state and Yjs
routeData. When a participant enables/disables POI categories, the
change propagates to all connected clients. Initial state loaded from
Yjs on connect. Crash recovery included via existing Yjs localStorage
snapshot.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
