fix: SSO on web

lib/config/app_config.dart

@@ -18,6 +18,7 @@ abstract class AppConfig {
   static String get privacyUrl => _privacyUrl;
   static const String appId = 'im.fluffychat.FluffyChat';
   static const String appOpenUrlScheme = 'im.fluffychat';
+  static const String webBaseUrl = 'https://fluffychat.im/web';
   static const String sourceCodeUrl = 'https://gitlab.com/famedly/fluffychat';
   static const String supportUrl =
       'https://gitlab.com/famedly/fluffychat/issues';

lib/pages/homeserver_picker.dart

@@ -198,7 +198,7 @@ class HomeserverPickerController extends State<HomeserverPicker> {
           ssoHomeserverKey, Matrix.of(context).client.homeserver.toString());
     }
     final redirectUrl = kIsWeb
-        ? html.window.location.href
+        ? AppConfig.webBaseUrl
         : AppConfig.appOpenUrlScheme.toLowerCase() + '://login';
     launch(
       '${Matrix.of(context).client.homeserver?.toString()}/_matrix/client/r0/login/sso/redirect/${Uri.encodeComponent(id)}?redirectUrl=${Uri.encodeQueryComponent(redirectUrl)}',