Implement Two-Factor Authentication (2FA) using Devise

[loftwah]

To enhance the security of our Linkarooie application, we need to implement two-factor authentication (2FA) using Devise. This will provide an additional layer of security for our users' accounts.

Tasks:

1. Add the necessary gems to support 2FA with Devise (e.g., devise-two-factor, rqrcode)
2. Generate and run the required migrations for 2FA
3. Update the Devise User model to include 2FA functionality
4. Modify the registration process to allow users to set up 2FA
5. Create views for 2FA setup and verification
6. Implement the 2FA verification process during login
7. Add option for users to disable 2FA if desired
8. Provide backup codes for account recovery
9. Update user documentation to explain 2FA setup and usage
10. Test thoroughly, including edge cases and potential security vulnerabilities

This feature will significantly improve the security of our application, giving users more control over their account protection.