feat: add GET /health endpoint

[Nishal77]

Summary

Adds a GET /health endpoint to the local FaaS server. Returns JSON with service status, version, uptime, timestamp, runtime identifier, and heap/RSS memory usage in MB.

Type of change

• Bug fix
• New feature
• Documentation
• Chore / CI
• Breaking change

How to test

1. Checkout the branch
2. Run npm ci
3. Run npm start
4. In another terminal: curl http://localhost:9000/health
5. Verify HTTP 200 with JSON body containing status, version, uptime, timestamp, runtime, memory

Checklist

• I have read the contributing guidelines
• I added tests that prove my fix is effective or that my feature works
• I updated documentation if necessary

Notes for reviewers

Registered in src/api.ts before the catch-all app.all('*') middleware. Router isolated in src/routes/health.ts. No new dependencies added.