feat: complete MDX migration, stabilize environment & verify via E2E tests

Former-commit-id: ec3e64156a2e182535cbdcf0d975cd54603a517d

app/[locale]/contact/page.tsx

@@ -62,7 +62,8 @@ export default async function ContactPage({ params }: ContactPageProps) {
   setRequestLocale(locale);
   const t = await getTranslations({ locale, namespace: 'Contact' });
 
-  // Get translated slug to redirect if user used incorrect static slug
+  // Get translated slug - redirect logic removed to prevent loop with next.config.js rewrites
+  /*
   const { headers } = await import('next/headers');
   const headersList = await headers();
   const urlPath = headersList.get('x-invoke-path') || '';
@@ -75,6 +76,7 @@ export default async function ContactPage({ params }: ContactPageProps) {
       redirect(`/${locale}/${contactSlugDe}`);
     }
   }
+  */
 
   return (
     <div className="flex flex-col min-h-screen bg-neutral-light">