Implement JWT Authentication for Secure API Access

Implement JWT authentication in the backend (Flask) to secure API access and ensure only authorized requests from the frontend (Axios) are allowed.

Tasks:

• Add flask-jwt-extended to handle authentication.
• Create /login endpoint to issue JWT tokens.
• Protect API routes with @jwt_required().
• Implement token expiration and refresh logic.
• Integrate JWT handling in frontend requests using Axios.

Acceptance Criteria:

• Users receive a JWT token upon successful login.
• Protected routes allow only authenticated requests.
• Expired tokens can be refreshed securely.
• Unauthorized requests return proper HTTP status codes.