Add index.js entry point to client/src for React application

- Created index.js in client/src as the main entry point for the React application.
- Ensures that the React build process can find the required entry file to complete successfully.
- Set up basic ReactDOM render logic, importing the main App component and rendering it to the root div in index.html.

This update resolves build errors related to the missing index.js file in the client/src directory.

Author: KazerL

client/src/index.js

@@ -0,0 +1,10 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+import App from './App';
+
+ReactDOM.render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>,
+  document.getElementById('root')
+);