ReFocus Web App: Backend and Auth Overhaul

I’m building ReFocus, a digital-wellness web app for students, and I need an experienced Node.js / Express / MongoDB developer (full-stack is a plus) to finish and fix the backend + role-based flows. Current status Frontend: React + Vite, deployed on Vercel (working). Backend: Node.js, Express, Mongoose, JWT auth, MongoDB Atlas. Basic auth routes exist but are incomplete/buggy. User roles: admin, coach, user. What I need Review and clean up existing backend code and API structure. Fix and finalize authentication & authorization: Login / register Email / password rules (simpler rules) Proper role-based access so each role only sees their own dashboard and pages (admin dashboard, coach dashboard, normal user pages). Implement / complete main features: User profile & survey data Challenges system (CRUD + assigning challenges to users) Coach application & approval flow by admin Any missing endpoints used by the frontend. Improve error handling and consistent API responses for all pages. Connect backend with existing frontend (update endpoints if needed). Basic tests + documentation (README with how to run the project). Help me deploy the backend (Render/other) so it works with my Vercel frontend. Requirements Strong experience with Node.js, Express, MongoDB, Mongoose, JWT. Comfortable working with an existing codebase and explaining changes. Communicate clearly and share work through Git/GitHub.