fix(dev): veralteten PWA-Cache bereinigen, damit i18n-Labels laden

Stale Service-Worker-Precache konnte Vite-Module und Locale-Bundles
überlagern, sodass Kompass-Dial-Texte als Roh-i18n-Keys erschienen.

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

client/src/i18n/index.ts

@@ -1,19 +1,26 @@
 import i18n from 'i18next'
 import { initReactI18next } from 'react-i18next'
 import LanguageDetector from 'i18next-browser-languagedetector'
-import enTranslation from './locales/en.json'
-import deTranslation from './locales/de.json'
+import enJson from './locales/en.json'
+import deJson from './locales/de.json'
 import { initSeo } from '../utils/seo.js'
 
+/** JSON files wrap strings in `translation` — register that namespace explicitly. */
+const resources = {
+  en: { translation: enJson.translation },
+  de: { translation: deJson.translation }
+}
+
 i18n
   .use(LanguageDetector)
   .use(initReactI18next)
   .init({
-    resources: {
-      en: enTranslation,
-      de: deTranslation
-    },
+    resources,
+    defaultNS: 'translation',
     fallbackLng: 'en',
+    supportedLngs: ['de', 'en'],
+    nonExplicitSupportedLngs: true,
+    load: 'languageOnly',
     interpolation: {
       escapeValue: false // React already escapes values (prevents XSS)
     },