chatgui: add shutdown diagnostics (poll exit reason, cleanup steps, app.exec return)

tools/chatgui/src/mainwindow.cpp

@@ -88,6 +88,7 @@ MainWindow::~MainWindow() {
     if (m_messageList) m_messageList->saveChannelState();
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — stopping utun node");
     if (m_node) { m_node->stop(); delete m_node; m_node = nullptr; }
+    DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — node stop+delete done");
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow done");
 }