Liveness/observability endpoint that survives the Cloud Run frontend.

Google Front End intercepts /healthz on *.run.app URLs for its own health checks, so a request to /healthz never reaches the container (see the smoke comment in scripts/deploy_cloud_run.sh). /status does reach the app, so it can report what's actually running: the live revision, process uptime, and the model from the GCS agent settings the widget actually uses.