fix: address unimplemented/broken issues across server and desktop

desktop/test/support.dart

@@ -0,0 +1,14 @@
+// 集成测试共享工具。
+import 'package:web_socket_channel/io.dart';
+
+/// 探测 Rtty 服务端是否可达；返回 false 时集成测试应被跳过。
+Future<bool> isServerUp(String host, int port) async {
+  try {
+    final ws = IOWebSocketChannel.connect(Uri.parse('ws://$host:$port/ws'));
+    await ws.ready.timeout(const Duration(seconds: 2));
+    ws.sink.close();
+    return true;
+  } catch (_) {
+    return false;
+  }
+}