refine nginx caching strategy and add service worker update prompt with periodic checks

frontend/vite.config.ts

@@ -9,10 +9,11 @@ export default defineConfig({
     react(),
     tailwindcss(),
     VitePWA({
-      registerType: 'autoUpdate',
+      registerType: 'prompt',
       manifest: false, // manifest.json from public
       workbox: {
         globPatterns: ['**/*.{js,css,html,ico,png,svg,json}'],
+        cleanupOutdatedCaches: true,
         runtimeCaching: [
           {
             urlPattern: /^https:\/\/.*\/api\//,