fix(chatgui): remove duplicate loadChannels after JoinDialog close, remove 800ms delay

- showJoinDialog: don't call loadChannels after dialog close — channel already in model via CHANNEL_UPDATED event, online badge via CHANNEL_PEERS_ONLINE. Duplicate loadChannels was resetting the peer online count.
- onConnectResult: remove 800ms QTimer — dialog closes immediately. Channel data arrives independently through the event pipeline.

tools/chatgui/src/mainwindow.cpp

@@ -267,8 +267,7 @@ void MainWindow::showJoinDialog() {
     }
 
     JoinDialog dlg(m_node, m_db, this, autoLink);
-    if (dlg.exec() == QDialog::Accepted)
-        m_channelList->loadChannels();
+    dlg.exec();
 }
 
 void MainWindow::showSettings() {