feat: flutter ui integration

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

@@ -0,0 +1,24 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'server_config.g.dart';
+
+@JsonSerializable()
+class ServerConfig {
+  late String host;
+  late int port;
+  late int connections;
+  late String downloadDir;
+  Map<String, dynamic>? extra;
+
+  ServerConfig({
+    required this.host,
+    required this.port,
+    required this.connections,
+    required this.downloadDir,
+    this.extra,
+  });
+
+  factory ServerConfig.fromJson(Map<String, dynamic> json) =>
+      _$ServerConfigFromJson(json);
+  Map<String, dynamic> toJson() => _$ServerConfigToJson(this);
+}