Build Health Check and Observability Module

[Mkalbani]

Description

Implement a health module that exposes readiness and liveness endpoints, along with basic observability hooks. In a production API, especially one with on-chain integrations, knowing the service is healthy and its dependencies are reachable is critical. This module ensures the API is production-operable from day one.

Acceptance Criteria

• A health module is scaffolded at src/health/
• GET /health/live returns 200 if the process is running
• GET /health/ready checks DB connectivity and returns 200 or 503 accordingly
• Response includes individual dependency statuses (db, cache if applicable)
• Health endpoints are excluded from JWT authentication
• Unhealthy dependencies return a structured error body, not a plain 500
• Request logging middleware logs method, path, status, and duration for every request
• Unit tests cover healthy state, DB failure simulation, and response structure