Abhi9835004352/HalcyonBackend — reverse-engineered prompt

Build me a simple backend for a project called Halcyon. I want a clean Express server connected to MongoDB, with basic user management that actually works end to end. It should let me list users, get one user by id, create a user, update a user, and delete a user through REST API routes. Please set up the usual controller, model, route, config, and error handling pieces so it feels organized and easy to extend later.

Make sure it reads environment variables for the port, database connection, and environment mode. I also want it easy to run locally and ready to deploy without a lot of extra setup. If there are helper scripts for things like creating an admin user or fixing database indexes, include those in a sensible way and keep them usable.

Please add basic validation, clear error responses, and enough test or sample scripts so I can quickly verify the API is working. Keep the code straightforward and practical. If you need to, look up current docs online and fill in any missing details.