feat: Add WFW-Aushang web app with PWA support, offline caching, and dark mode

- Created index.html for the main application interface with responsive design and dark mode support.
- Added manifest.webmanifest for PWA configuration, including app icons and display settings.
- Implemented service worker (sw.js) for offline caching of assets and network-first strategy for versioning.
- Introduced version.json to manage app versioning.

bibel-pwa/service-worker.js

@@ -0,0 +1,68 @@
+/*
+ * Service Worker für die Bibel Lern‑App
+ * Dieser Worker sorgt dafür, dass die wesentlichen Dateien
+ * für den Offline‑Betrieb zwischengespeichert werden und
+ * veraltetete Caches bereinigt werden.
+ */
+
+const CACHE_NAME = 'bibel-app-cache-v3';
+// Arbeite mit relativen Pfaden, damit die PWA auch aus einem Unterordner funktioniert.
+const BASE_PATH = new URL(self.registration.scope).pathname.replace(/\/$/, '');
+const scopePath = (path) => `${BASE_PATH}/${path}`;
+const OFFLINE_URLS = [
+  'index.html',
+  'styles.css',
+  'script.js',
+  'manifest.json',
+  'data.json',
+  'data.csv',
+  'icon-192x192.png',
+  'icon-512x512.png'
+].map(scopePath);
+
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => {
+      return cache.addAll(OFFLINE_URLS);
+    })
+  );
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((cacheNames) => {
+      return Promise.all(
+        cacheNames.map((cacheName) => {
+          if (cacheName !== CACHE_NAME) {
+            return caches.delete(cacheName);
+          }
+        })
+      );
+    })
+  );
+});
+
+self.addEventListener('fetch', (event) => {
+  if (event.request.method !== 'GET') return;
+  const requestUrl = new URL(event.request.url);
+
+  // Nur Anfragen innerhalb des eigenen Ursprungs beantworten, damit Offsite‑Requests
+  // nicht ungewollt überschrieben werden.
+  if (requestUrl.origin !== self.location.origin) return;
+
+  event.respondWith(
+    caches.match(event.request).then((cached) => {
+      if (cached) return cached;
+      return fetch(event.request).catch(() => {
+        // Fallback bei HTML‑Anfragen
+        if (
+          event.request.mode === 'navigate' ||
+          event.request.headers.get('accept')?.includes('text/html')
+        ) {
+          return caches.match(scopePath('index.html'));
+        }
+      });
+    })
+  );
+});
+