Enhance error response handling in WebSocket server

- Add detailed logging for error responses during WebSocket callbacks, improving visibility into the error handling process.
- Ensure that error responses are queued correctly without immediate sending, enhancing stability during callback execution.
- Utilize lws_cancel_service to notify the service of pending messages, ensuring proper message delivery after error handling.

src/websocket_server.cpp

@@ -325,21 +325,26 @@ int WebSocketServer::wsCallback(struct lws *wsi,
                             // Sende Fehlerantwort nicht während des Callbacks, sondern lege sie in die Queue
                             // und triggere den WRITEABLE-Callback später
                             try {
+                                std::cout << "[RECEIVE] getConnections: make response" << std::endl;
                                 json errorResponse = {
                                     {"event", "getConnectionsResponse"},
                                     {"success", false},
                                     {"error", "User-ID nicht gesetzt"}
                                 };
+                                std::cout << "errorResponse: " << errorResponse.dump() << std::endl;
                                 if (instance && wsi && ud) {
+                                    std::cout << "instance: " << instance << std::endl;
                                     // Lege Nachricht in die Queue, ohne sofort lws_callback_on_writable aufzurufen
                                     {
                                         std::lock_guard<std::mutex> lock(ud->messageQueueMutex);
                                         ud->messageQueue.push(errorResponse.dump());
                                     }
+                                    std::cout << "ud->messageQueue.size(): " << ud->messageQueue.size() << std::endl;
                                     // Verwende lws_cancel_service, um den Service zu benachrichtigen
                                     if (instance->context) {
                                         lws_cancel_service(instance->context);
                                     }
+                                    std::cout << "lws_cancel_service(instance->context) done" << std::endl;
                                 }
                             } catch (const std::exception &e) {
                                 std::cerr << "[RECEIVE] Fehler beim Senden der Fehlerantwort: " << e.what() << std::endl;