Implement Authentication System

[A23droid]

Description

Add a user authentication system that allows registration, login, and logout. Ensure the frontend only allows authorized access to habit-related pages.

Acceptance Criteria

• Users can register and log in successfully.
• Users can log out, and unauthorized access is blocked.
• Implementation method is flexible (JWT, session, OAuth, etc.).
• Authentication integrates cleanly with the existing frontend routing.
• System handles invalid credentials and shows proper error messages.