Honest health checks

Design and verify service health endpoints that report REAL readiness (database and critical dependencies reachable) instead of a hardcoded 200, and wire them correctly into deploy gates, container HEALTHCHECKs, and orchestrator probes. Use this whenever you add or review a /health or /healthz endpoint, set up a Docker/Kubernetes/compose health check or a post-deploy probe, or when the user asks "why did the deploy go green but the app is down?", "add a readiness probe", "make the health check honest", or is debugging a service that's "up" but not actually serving. A health endpoint that returns 200 unconditionally silently defeats every gate built on it - so make it asse…