Readiness probe

Readiness probe.

Returns 200 OK if the service is ready to process requests. Returns 503 Service Unavailable if storage is not available.

This endpoint verifies that:

• the storage backend answers a real health check
• the integrator store the auth middleware needs is wired

It deliberately takes NO injected dependency. FastAPI resolves those before the handler body, outside the try below, and get_pot_service raises RuntimeError when app.state.pot_service is missing — so a partially wired app answered 500 from the endpoint whose whole job is to answer 503 with a reason. Everything it needs is read off request.app.state inside the guard.