feat: add request/response logging middleware

[Nishal77]

Summary

Adds src/middleware/requestLogger.ts logs every HTTP request on response finish with method, path, status code, and duration in ms. Uses process.hrtime.bigint() for nanosecond precision. No new dependencies.

Related issue

Fixes #153

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. Check server terminal for: [GET] /health 200 1.23ms

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 immediately after express.json() and express.urlencoded() so it runs before all routes
• Uses res.on('finish') — logs after response sent, never blocks request handling
• No colors, no ANSI codes, plain text only

Release notes

All incoming requests now logged to stdout with method, path, status, and duration in ms.