[TEMPLATE] - React-Native+Express-Backend

### What domain will the project template be based on?

Others (please specify in the details)

### If 'Others', please specify the preferred domain.

Mobile Application Development

### Particular directory path for the template.

template/Mobile/React-Native+Express-Backend/

### What tech stacks do you want to include?

- Frontend (Mobile App): React Native
- Backend (API): Express.js (Node.js)
- Database: MongoDB (via Mongoose ORM)
- Networking: Axios for REST API integration
- Auth: JWT-based authentication setup
- Dev Tools: Nodemon, ESLint

### Brief Description

This template scaffolds a Mobile Hybrid App built with React Native for the frontend and Express.js for the backend API.

It enables developers to quickly build mobile applications that communicate with a robust backend server out-of-the-box.

The template will include:
- A pre-configured Express API with sample routes and JWT authentication.
- A React Native mobile interface (login/signup screen, API integration examples).
- Folder structure optimized for scalability (frontend and backend separated).
- Ready-to-run instructions and scripts for local development (`npm run dev` / `yarn start`).

This will help developers prototype full-stack mobile apps instantly using the `universal-box init` command, eliminating the hassle of configuring mobile-backend integration manually.

### 👀 Have you spent some time checking if this issue has been raised before?

- [x] Yes
- [ ] No

### 🏢 Have you read the Code of Conduct?

- [x] I have read the [Code of Conduct](https://github.com/Abhishek-Mallick/universal-box/blob/main/.github/CODE_OF_CONDUCT.md)

### Would you like to work on this issue?

No

The template should be created in the directory 'template/Mobile/React-Native+Express-Backend/'. Start by examining existing templates in the repository to understand the structure and required files. The template needs to include separate frontend (React Native) and backend (Express.js with MongoDB) setups with authentication and example screens. Check the 'universal-box init' command to see how templates are used. Ensure the template includes clear setup instructions and run scripts.

索引モデルが issue の本文から書いたものです。