feat: flutter ui integration

ui/flutter/lib/api/model/request.dart

@@ -0,0 +1,18 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'request.g.dart';
+
+@JsonSerializable()
+class Request {
+  String url;
+  Map<String, dynamic>? extra;
+
+  Request({
+    required this.url,
+    this.extra,
+  });
+
+  factory Request.fromJson(Map<String, dynamic> json) =>
+      _$RequestFromJson(json);
+  Map<String, dynamic> toJson() => _$RequestToJson(this);
+}