📁 Folder Structure (Backend)

A modular and organized structure:

/src
  /controllers   # Logic for handling routes
  /models        # Mongoose/Firebase models (User, Course, Certificate, etc.)
  /routes        # API routes
  /middleware    # Auth, validation
  /services      # Business logic, DB interactions
  /utils         # Helpers, constants
/app.js          # Express app setup
/config          # Environment and DB config