Show accepted signup delivery without a second send step (#62)

frontend/app/lib/auth/form.dart

@@ -99,10 +99,11 @@ class _AuthFormState extends State<AuthForm> {
         return;
       }
       final email = _email.text.trim();
+      final delivery = signup.state.result!.delivery;
       TextInput.finishAutofillContext();
       _password.clear();
       _confirmation.clear();
-      context.goNamed(AppRoutes.verificationSent, extra: email);
+      context.goNamed(AppRoutes.verificationSent, extra: delivery ?? email);
     } else {
       final login = context.read<LoginProvider>();
       await login.login(