add pwa

frontend/src/main.tsx

@@ -3,6 +3,18 @@ import { createRoot } from 'react-dom/client'
 import './index.css'
 import App from './App.tsx'
 
+if ('serviceWorker' in navigator) {
+  window.addEventListener('load', () => {
+    navigator.serviceWorker.register('/sw.js', { scope: '/' })
+      .then((registration) => {
+        console.log('SW registered:', registration)
+      })
+      .catch((error) => {
+        console.log('SW registration failed:', error)
+      })
+  })
+}
+
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
     <App />