Flatten budget-app contents into repo root

frontend/src/main.jsx

@@ -0,0 +1,13 @@
+import React from 'react'
+import { createRoot } from 'react-dom/client'
+import { BrowserRouter } from 'react-router-dom'
+import App from './App.jsx'
+import './styles.css'
+
+createRoot(document.getElementById('root')).render(
+  <React.StrictMode>
+    <BrowserRouter>
+      <App />
+    </BrowserRouter>
+  </React.StrictMode>,
+)