fix(pwa): Startup-Hänger nach Inaktivität stabilisieren

Verhindert Blank-Screens und Reload-Schleifen beim Wiederöffnen der PWA, indem Recovery nur bei bestätigter SW-Übernahme greift und Navigationen bevorzugt frisch aus dem Netzwerk geladen werden.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/sw.ts

@@ -1,11 +1,25 @@
 /// <reference lib="webworker" />
 import { clientsClaim } from 'workbox-core'
-import { cleanupOutdatedCaches, precacheAndRoute } from 'workbox-precaching'
+import { cleanupOutdatedCaches, createHandlerBoundToURL, precacheAndRoute } from 'workbox-precaching'
 import { registerRoute } from 'workbox-routing'
-import { NetworkOnly } from 'workbox-strategies'
+import { NetworkFirst, NetworkOnly } from 'workbox-strategies'
 
 declare let self: ServiceWorkerGlobalScope
 
+const appShellFallback = createHandlerBoundToURL('/index.html')
+const navigationStrategy = new NetworkFirst({
+  cacheName: 'app-shell',
+  networkTimeoutSeconds: 3
+})
+
+registerRoute(({ request }) => request.mode === 'navigate', async (context) => {
+  try {
+    return await navigationStrategy.handle(context)
+  } catch {
+    return appShellFallback(context)
+  }
+})
+
 precacheAndRoute(self.__WB_MANIFEST)
 cleanupOutdatedCaches()
 clientsClaim()