Prepare Kalendartool for MPM and disable invites

components/admin/EditCalendarModal.tsx

@@ -15,6 +15,7 @@
  * Dashboard verwendet (DRY). Schliessen via X-Icon, ESC oder
  * Hintergrund-Klick; waehrend des Speicherns ist Schliessen blockiert.
  */
+import { appFetch } from '@/lib/client-fetch';
 import { useState } from 'react';
 import { useRouter } from 'next/navigation';
 import { Button, ErrorMessage, Input, Label } from '@/components/ui/ui';
@@ -61,7 +62,7 @@ export function EditCalendarModal({
 
     const formData = new FormData(event.currentTarget);
     try {
-      const response = await fetch(`/api/calendars/${calendar.id}`, {
+      const response = await appFetch(`/api/calendars/${calendar.id}`, {
         method: 'PATCH',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({