Keep the window responsive while the channel tree loads

Connecting to a server with ~560 channels froze the UI for over two
seconds: every model event queued its own full tree rebuild, and each
rebuild expanded row by row with Swing's variable-height layout cache,
which measures every row on each expansion.

Coalesce model-change bursts into one rebuild and switch the tree to the
large-model layout (it already has a fixed row height), which only
measures rows on screen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ts3-client/swing/src/main/java/com/ts3client/ui/ServerTabConnectionEvents.java

@@ -8,6 +8,7 @@ import com.ts3client.net.TeamspeakConnection;
 import javax.swing.JOptionPane;
 import javax.swing.SwingUtilities;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * Marshals {@link ConnectionListener} callbacks onto the EDT and fans them out to
@@ -32,6 +33,8 @@ final class ServerTabConnectionEvents implements ConnectionListener {
     private final ServerTab tab;
     private final Listener listener;
 
+    private final AtomicBoolean modelChangePending = new AtomicBoolean();
+
     private TeamspeakConnection conn;
     private ServerTreePanel treePanel;
     private ChatPanel chatPanel;
@@ -101,7 +104,10 @@ final class ServerTabConnectionEvents implements ConnectionListener {
 
     @Override
     public void onModelChanged() {
+        // Events arrive in bursts (hundreds while connecting); one rebuild covers all of them.
+        if (!modelChangePending.compareAndSet(false, true)) return;
         SwingUtilities.invokeLater(() -> {
+            modelChangePending.set(false);
             treePanel.rebuild();
             treeActions.renderInfo();
             treeActions.refreshGroupsDialog();

ts3-client/swing/src/main/java/com/ts3client/ui/ServerTreePanel.java

@@ -170,6 +170,9 @@ public final class ServerTreePanel extends JScrollPane {
             ui.setRightChildIndent(10);
         }
         tree.setRowHeight(UIScale.scale(20));
+        // Lays out only the rows on screen. The default cache measures every row as it is
+        // expanded, which freezes the window for seconds on servers with hundreds of channels.
+        tree.setLargeModel(true);
         tree.setBackground(Theme.treeBg());
         tree.setFont(Theme.uiFont());
         ServerTreeCellRenderer renderer = new ServerTreeCellRenderer(id -> id == selfClientId, contacts, settings);