siddhartha12hr-crypto/Mern ? reverse-engineered prompt

Build me a simple full stack MERN app with a frontend and a backend that work together smoothly.

I want a clean modern app where users can sign up, log in, and manage some basic data in a dashboard style interface. The frontend should feel polished and easy to use, with forms, navigation, and a few useful screens that make the app feel complete. The backend should handle authentication, store data safely, and expose the needed API endpoints so the frontend can talk to it without issues.

Please wire everything up so it runs as one project, with clear setup instructions and sensible defaults. If you need to look up current docs online to make sure the code is up to date, go ahead. Keep the code organized and simple enough that I can extend it later. Also make sure errors are handled nicely and the app does not feel broken if something goes wrong.