Feat: Implement authentication system

[Upendra48]

• Added JWT token generation utilities with generate_access_token and generate_refresh_token in jwt_utils.py, using a secret key from environment variables or Django settings.

• Implemented password hashing and verification using bcrypt in utils.py to securely store and compare user passwords.

• Created service functions in services.py for registering users (with default board/columns creation) and logging in users (with JWT issuance).

• Added a jwt_required decorator in middleware.py to protect endpoints by validating JWTs and attaching the user to the request.

• Added API endpoints in views.py for user registration, login, and fetching the current user, integrating the above services and middleware.