chatgui: invite link connect flow + GUI_ERROR always-on diagnostics

- debug_ui.h: remove NDEBUG guard so GUI_ERROR works in Release builds
- invite_link.h/cpp: add error field to InviteData with specific failure reason
- joindialog: show exact decode error in QLabel instead of generic message
- chat_sync: implement invite connect flow (CHANNEL_INFO_REQ/RESP, JOIN, WELCOME)
- topo_node_sqlite: node/address table init and lookup
- utun_node: getInviteAddresses fallback from ETCP sockets
- minor fixes in mainwindow, chat_core, gui_bridge

tools/chatgui/src/mainwindow.cpp

@@ -205,9 +205,9 @@ void MainWindow::showInviteDialog(const QString& channelId) {
         return;
     }
 
-    QList<NodeAddr> addrs = m_db->getOnlinePeerAddresses(m_db->myNodeId());
+    QList<NodeAddr> addrs = m_node->getInviteAddresses(m_db);
 
-    QString link = encodeInviteLink(channelId, pubkey, addrs);
+    QString link = encodeInviteLink(channelId.toULongLong(), pubkey, addrs);
     if (link.isEmpty()) {
         QMessageBox::warning(this, "Error", "Failed to create invite link.");
         return;