Noman-dev3/My-mart-POS ? reverse-engineered prompt

Build me a clean authentication flow for a small shop POS app in this Next.js project.

I want a centered login and sign up screen that feels polished on mobile and desktop, with a simple card layout, light and dark mode styling, and a smooth switch between signing in and creating an account. The sign up form should ask for first name, last name, email, password, and a terms and conditions checkbox, while the login form only needs email and password. Add basic validation, helpful error messages, loading states on submit, and toast messages for success or failure.

Please also include a Google sign in button, and make the auth page feel friendly and modern. If anything needs current docs or best practice details, look it up online before wiring it in.