fix race condition: DB_READY lost when utun thread starts before gui_bridge_init

- mainwindow.cpp: swap setupMessaging() before setupNode() so g_receiver is created first
- gui_bridge_impl.cpp: add DEBUG_WARN when gui_bridge_post drops event due to NULL g_receiver

tools/chatgui/transport/gui_bridge_impl.cpp

@@ -151,7 +151,7 @@ void gui_bridge_set_uasync(struct UASYNC* ua) {
 }
 
 void gui_bridge_post(int event_type, const uint8_t* data, int data_len) {
-    if (!g_receiver) return;
+    if (!g_receiver) { DEBUG_WARN(DEBUG_CATEGORY_DEBUG, "gui_bridge_post: g_receiver=NULL, dropping event %d", event_type); return; }
 
     QByteArray d;
     if (data_len > 0) d = QByteArray((const char*)data, data_len);