soumen31/Mern-Ecommerce ? reverse-engineered prompt

Build me the backend for a simple ecommerce app. I want a working API that can handle user sign up and login, products, categories, cart, orders, and basic admin actions like adding, editing, and deleting products.

Make it feel like a real store backend, with clean routes, controllers, and data models, and include validation and error handling so it does not break on bad requests. Use a database and make sure the app can store users, products, and orders properly. If you need to check the latest docs for anything, go ahead and look them up online.

Please also add a simple way to test the API, either with sample data or a few example requests, and make the project easy to run locally with clear setup steps. If there is any missing piece, choose sensible defaults and keep it practical.