chore: validate domain on server

apps/dashboard/src/routes/api/domain/+server.ts

@@ -17,6 +17,10 @@ export async function POST({ request }) {
     return json({ success: false, message: 'Missing fields' }, { status: 400 });
   }
 
+  if (params?.domain?.includes('classroomio')) {
+    return json({ success: false, message: 'Domain cannot contain classroomio' }, { status: 400 });
+  }
+
   let user;
   try {
     const { data } = await supabase.auth.getUser(accessToken);