[SECURITY] Implement API Rate Limiting

[vallabhatech]

Description

The application currently lacks protection against brute-force attacks or Denial of Service (DoS). Any user or bot can hit the login or registration endpoints indefinitely.

Proposed Fix

Integrate express-rate-limit as a middleware.

• Limit general API hits to 100 per 15 minutes.
• Limit Auth routes (Login/Register) to 5 attempts per 15 minutes.

Test Cases

• TC1 (Normal Usage): Send 10 requests to /api/v1/users/login. Verify all receive 200 or 401 status codes.
• TC2 (Rate Limit Trigger): Send 100+ requests rapidly. Verify the server returns 429 Too Many Requests.
• TC3 (Reset logic): Wait for the limit duration (15 mins) and verify access is restored.