feat(security): Implement rate limiting for login endpoint

[Zafar7645]

The POST /auth/login endpoint currently lacks protection against brute-force attacks. This is a potential security vulnerability.

Tasks:

• Integrate the @nestjs/throttler package.
• Apply rate limiting specifically to the /auth/login route.
• Configure the limit to a reasonable value (e.g., ~5-10 attempts per minute per IP).
• (Optional: Consider adding account lockout logic after a higher number of repeated failures).

This will help mitigate brute-force password guessing attacks.