Prepare Kalendartool for MPM and disable invites

components/admin/CalendarManager.tsx

@@ -9,6 +9,7 @@
  *  - "Kalender erstellen" oeffnet ein Erstellen-Modal (POST /api/calendars).
  *  - Alle Modals sind per X-Icon, ESC und Hintergrund-Klick schliessbar.
  */
+import { appFetch } from '@/lib/client-fetch';
 import { useState } from 'react';
 import { useRouter } from 'next/navigation';
 import { Button, Card, ErrorMessage, Input, Label } from '@/components/ui/ui';
@@ -66,7 +67,7 @@ export function CalendarManager({
     setIsPending(true);
     setError(null);
     try {
-      const response = await fetch('/api/calendars', {
+      const response = await appFetch('/api/calendars', {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify(values),