Making backend for authentication

## Description
The project currently has a working frontend but lacks a backend to handle authentication and data storage. We need to implement a backend using **Node.js**, **Express.js**, and **MongoDB** to manage user authentication and related API functionality.

## Steps to Reproduce
1. Run the frontend.
2. Try to sign up or log in.
3. Notice there’s no backend to handle authentication requests.

## Expected Behavior
There should be a backend service that:
- Connects to a MongoDB database.
- Provides API endpoints for user registration, login, and authentication.
- Supports JWT-based session management.
- Can be easily integrated with the existing frontend.

## Actual Behavior
The frontend works well, but there’s currently no backend to support authentication or database operations.

## Additional Info
The backend should follow RESTful principles and be structured for scalability.