minor fixes

lib/screens/gateway/gateway_screen.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
-import 'package:flutter_dotenv/flutter_dotenv.dart';
 import 'package:go_router/go_router.dart';
+import 'package:qpay/config/app_config.dart';
 import 'package:qpay/screens/gateway/gateway_controller.dart';
 import 'package:qpay/widgets/app_snack_bar.dart';
 import 'package:webview_flutter/webview_flutter.dart';
@@ -56,7 +56,7 @@ class _GatewayScreenState extends State<GatewayScreen> {
       )
       ..loadRequest(Uri.parse(url));
 
-    bool simulate = bool.parse(dotenv.env['SIMULATE_PAYMENT_SUCCESS']!);
+    bool simulate = AppConfig.simulatePaymentSuccess;
     if (simulate) {
       await Future.delayed(Duration(seconds: 10));
       String targetUrl = url.replaceAll("/pay/", "/receipt/");