feat(auth): implement rate limiting for authentication endpoints

[Devsol-01]

feat(auth): implement rate limiting for authentication endpoints

Description

This PR introduces rate limiting for the authentication endpoints to improve security and protect against brute-force and denial-of-service attacks.

What's Changed

• Added rate limiting to the login endpoint.
• Added rate limiting to the signup endpoint.
• Implemented exponential backoff after repeated failed attempts.
• Integrated Redis for distributed rate limit storage.
• Configured separate limits for login and signup requests.
• Added middleware to handle rate limit responses consistently.

Why

Authentication endpoints are common targets for brute-force attacks. This implementation helps mitigate abuse while maintaining a good user experience for legitimate users.

Testing

• Verified login rate limiting after the configured number of failed attempts.
• Verified signup rate limiting.
• Confirmed lockout duration is enforced correctly.
• Tested successful requests after the lockout period expires.

Checklist

• Code follows project standards
• Tested locally
• No breaking changes introduced
• Documentation updated (if applicable)

closes #801
closes #802
closes #803
closes #804