Automatically put people into DTTHDon login

src/pages/login.jsx

@@ -24,7 +24,7 @@ function Login() {
   const instance = searchParams.get('instance');
   const submit = searchParams.get('submit');
   const [instanceText, setInstanceText] = useState(
-    instance || cachedInstanceURL?.toLowerCase() || '',
+    instance || cachedInstanceURL?.toLowerCase() || 'gts.dtth.ch',
   );
 
   const [instancesList, setInstancesList] = useState([]);