Local backend needs the cloud DB integer PK to call Connect API
endpoints (menu sync, order pending poll). Heartbeat is the only
authenticated channel available at startup, so we piggyback the id
there rather than adding a new endpoint.
Changes:
- schemas/site.py: site_numeric_id: int | None added to HeartbeatResponse
- routers/heartbeat.py: site_numeric_id=site.id included in response
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>