tejaspachgade2315/Backend-Gym — reverse-engineered prompt

Build me the backend for a simple Gym ERP in JavaScript. I want it to work like the admin system for a gym, where staff can manage gym members, membership plans, renewals, payments, trainers or staff records, and basic attendance or check ins if that fits the existing code.

Set up clean API routes, controllers, models, services, middleware, config, and utility files so it is easy to understand and extend. Add login and protected admin routes if the project already has auth patterns, with sensible validation and clear error messages.

Include Swagger API docs since there is already a swagger file, and make sure the server starts from index.js and can be deployed with the existing Render setup. Keep it simple but complete enough that someone can test all core flows with Postman or Swagger. If anything is missing from the README, use common Gym ERP behavior and look up current docs online if needed.