ed-roh/mern-social-media ? reverse-engineered prompt

Build me a complete full stack social media app that feels modern and polished.

I want users to be able to sign up, log in, and stay signed in, then create posts, like other posts, and browse a responsive feed that works well on desktop and mobile. Please include a clean dark mode toggle too, since that’s a big part of the experience. The app should look good out of the box, with a simple and friendly UI, and use a solid React front end with a MongoDB backed server for the data and auth.

Make it feel like a real working product, not just a demo. If you need to look up current docs or best practices while building, go ahead. Focus on the full experience, from the front end screens to the API and database wiring, and make sure the final result is easy to run and test locally.