Fix server GUI not exiting on KDE (#3016)

src/serverdlg.cpp

@@ -524,6 +524,13 @@ void CServerDlg::closeEvent ( QCloseEvent* Event )
 
     // default implementation of this event handler routine
     Event->accept();
+
+    // On some desktop environments (observed on KDE with Qt 5.15, Ubuntu 22.04+
+    // and Fedora 37+) closing the server GUI only hides the window while the
+    // process and system tray icon keep running (#3016). Explicitly quitting the
+    // application on close restores the expected behaviour. This is a pragmatic
+    // fix; a signals/slots-based shutdown may be the cleaner long-term solution.
+    QApplication::quit();
 }
 
 void CServerDlg::OnStartOnOSStartStateChanged ( int value )

src/serverdlg.h

@@ -46,6 +46,7 @@
 
 #pragma once
 
+#include <QApplication>
 #include <QCloseEvent>
 #include <QLabel>
 #include <QListView>