add flutter

ontime_merchant_flutter/lib/data/api/api_client.dart

@@ -0,0 +1,24 @@
+import 'package:dio/dio.dart';
+import 'package:ontime_merchant_flutter/core/app_config.dart';
+
+class ApiClient {
+  ApiClient({
+    required String? basicAuthUser,
+    required String? basicAuthPassword,
+  }) : _dio = Dio(
+          BaseOptions(
+            baseUrl: AppConfig.apiBase,
+            connectTimeout: const Duration(seconds: 15),
+            receiveTimeout: const Duration(seconds: 20),
+          ),
+        ) {
+    if (basicAuthUser != null && basicAuthPassword != null) {
+      final auth = '$basicAuthUser:$basicAuthPassword';
+      final encoded = String.fromCharCodes(auth.codeUnits);
+      _dio.options.headers['Authorization'] = 'Basic $encoded';
+    }
+  }
+
+  final Dio _dio;
+  Dio get raw => _dio;
+}