Health-check endpoints for Data services

We added first-class health endpoints to the Data query service so unhealthy instances can be detected and recycled automatically.

1. Dedicated liveness and readiness endpoints back standard container health probes.
2. The readiness check validates downstream connectivity before an instance starts accepting traffic.
3. Probes run independently of the main request path, so they stay responsive even when downstream systems are degraded.
4. Resolves a class of transient 404 errors caused by instances receiving traffic before they were fully warmed up.