feat(app): i18n-init registriert messages und syncs mit activeLocale

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/src/lib/i18n/index.ts

@@ -0,0 +1,23 @@
+import { addMessages, init, locale, _ } from 'svelte-i18n';
+import de from './messages/de.json';
+import en from './messages/en.json';
+import { activeLocale, SUPPORTED_LOCALES } from './activeLocale';
+
+let initialized = false;
+
+export function initI18n(): void {
+  if (initialized) return;
+  initialized = true;
+  addMessages('de', de);
+  addMessages('en', en);
+  init({
+    fallbackLocale: 'de',
+    initialLocale: 'de'
+  });
+  activeLocale.bootstrap();
+  activeLocale.subscribe((l) => {
+    locale.set(l);
+  });
+}
+
+export { _ as t, locale, activeLocale, SUPPORTED_LOCALES };