Add detailed health check endpoint with downstream service status monitoring

[amaydixit11]

Feature Request

Add a health check endpoint that verifies connectivity to ALL downstream services (Acadmap, CoSA, Smart Insti, Jobs, etc).

Problem

Currently the /health endpoint only reports whether Hub itself is up. It does not verify that downstream services are reachable or responding.

Proposed Solution

• GET /api/v1/health/detailed
• Returns status of each downstream service (reachable, response time, last error)
• Useful for SRE/ops dashboards
• The existing health module at src/health/health.controller.ts can be extended