Set up React application entry point

frontend/src/main.tsx

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