chatgui: synchronous DB write in saveChannelState/updateReadPosition, add shutdown debug logs

Replace gui_bridge_post_uasync_fn (async queue lost on shutdown) with direct
chat_core_save_ui_state (sync SQLite write). SQLite WAL handles concurrent access.
Add DEBUG_DEBUG traces in closeEvent, ~MainWindow, aboutToQuit.

tools/chatgui/src/mainwindow.cpp

@@ -85,7 +85,9 @@ MainWindow::MainWindow(QWidget *parent, DbManager* db, const QString& cfgPath,
 }
 
 MainWindow::~MainWindow() {
+    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 done");
 }
 
 void MainWindow::setupUi() {
@@ -230,7 +232,10 @@ void MainWindow::setupConnects() {
                         m_db->getUnreadCount(channelId, lastReadMsgId));
             });
 
-    connect(qApp, &QApplication::aboutToQuit, m_messageList, &MessageList::saveChannelState);
+    connect(qApp, &QApplication::aboutToQuit, this, [this]() {
+        DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: aboutToQuit — saving channel state");
+        if (m_messageList) m_messageList->saveChannelState();
+    });
 }
 
 void MainWindow::setupTray() {
@@ -263,6 +268,7 @@ void MainWindow::setupTray() {
 }
 
 void MainWindow::closeEvent(QCloseEvent *event) {
+    DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: closeEvent — hiding to tray");
     hide();
     m_trayIcon->showMessage("Chat", "Application minimized to tray.",
                              QSystemTrayIcon::Information, 2000);