Prepare Kalendartool for MPM and disable invites

prisma/seed-admin.cjs

@@ -26,6 +26,10 @@ async function seedAdmin() {
   const password = (process.argv[3] || process.env.SEED_ADMIN_PASSWORD || '').trim();
 
   if (!email || !password) {
+    if (!email && !password) {
+      console.log('[seed] Keine Admin-Startdaten konfiguriert; überspringe Seed.');
+      return;
+    }
     console.error(
       '[seed] Verwendung: node prisma/seed-admin.cjs <email> <passwort>\n' +
         '  oder: SEED_ADMIN_EMAIL=… SEED_ADMIN_PASSWORD=… node prisma/seed-admin.cjs',
@@ -75,4 +79,4 @@ seedAdmin()
   })
   .finally(async function () {
     await prisma.$disconnect();
-  });
+  });