chatgui: move SoundManager shutdown to ~MainWindow before node cleanup

- SoundManager::shutdown() called explicitly in ~MainWindow (not static destruction)
- Before ma_engine_uninit: DEBUG_INFO diagnostic in timestamped log
- After ma_engine_uninit: DEBUG_INFO diagnostic
- Double-call safe: static destructor hits m_initialized=false, returns immediately

tools/chatgui/src/mainwindow.cpp

@@ -84,6 +84,7 @@ MainWindow::MainWindow(QWidget *parent, DbManager* db, const QString& cfgPath,
 }
 
 MainWindow::~MainWindow() {
+    SoundManager::instance()->shutdown();
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — saving channel state");
     if (m_messageList) m_messageList->saveChannelState();
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — stopping utun node");