Working Signup/Auth System

PROJECT CONTEXT:
I am building a web app and need a complete working authentication flow.

GOAL:
Create real signup, login, session persistence, and protected routes.

REQUIREMENTS:
- Email/password signup with confirm password
- Login and logout
- Session persistence across page refresh
- Protected dashboard routes
- Validation and error states shown in the UI
- Duplicate email handling
- Password reset flow
- Mobile responsive UI

CONSTRAINTS:
- Do not create only visual forms
- Implement real persistence and user state
- Include clear loading and error behavior
- Never store plaintext passwords

DEFINITION OF DONE:
- New users can sign up and a real user record is created
- Users can log in and log out
- Session persists after refresh
- Logged-out users cannot access protected pages
- Duplicate email fails cleanly with a visible error
- Validation errors appear clearly in the UI
- Mobile layout works

COMMON FAILURES TO AVOID:
- AI creates a signup form with no real persistence
- Login button redirects visually but does not store session state
- Protected routes can still be opened while logged out
- Duplicate emails are not handled
- Errors only appear in console, not UI
- Session dies on refresh because nothing was persisted