blocked all nextcloud requests in demo mode to stop fake-credential logins tripping brute-force protection

lib/api/marianumcloud/webdav/webdav_api.dart

@@ -3,6 +3,8 @@ import 'package:nextcloud/nextcloud.dart';
 import '../../../model/endpoint_data.dart';
 import '../../../session/session_manager.dart';
 import '../../api_response.dart';
+import '../../demo/demo_mode.dart';
+import '../../errors/network_exception.dart';
 
 abstract class WebdavApi<T> {
   T genericParams;
@@ -18,6 +20,14 @@ abstract class WebdavApi<T> {
   /// changes (app password minted/renewed, account switch) so it never keeps
   /// authenticating with stale credentials.
   static Future<WebDavClient> get webdav {
+    // The WebDAV client talks dart:io directly, past DemoHttpClient.
+    if (DemoMode.active) {
+      return Future.error(
+        NetworkException.demoBlocked(
+          Uri.parse(EndpointData().nextcloud().origin()),
+        ),
+      );
+    }
     // Keyed by user too: two accounts may share a password (no app password
     // minted), and the client would keep the previous login name.
     final nextcloud = SessionManager().requireNextcloud();