Prepare Kalendartool for MPM and disable invites

app/login/page.tsx

@@ -3,6 +3,7 @@
 /**
  * Anmeldeseite (plan.md Abschnitt 11).
  */
+import { appFetch } from '@/lib/client-fetch';
 import { useState } from 'react';
 import { useRouter } from 'next/navigation';
 import Link from 'next/link';
@@ -20,7 +21,7 @@ export default function LoginPage() {
 
     const formData = new FormData(event.currentTarget);
     try {
-      const response = await fetch('/api/auth/login', {
+      const response = await appFetch('/api/auth/login', {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({