Open connection info by middle-clicking a client

The dialog now disposes when its window button is used, too: hiding it
left the one-second refresh timer polling the server for a window
nobody could see again.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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

@@ -151,11 +151,13 @@ public final class ServerTreePanel extends JScrollPane {
 
             @Override
             public void mouseClicked(MouseEvent e) {
+                Object obj = nodeAt(e);
                 if (SwingUtilities.isLeftMouseButton(e) && e.getClickCount() == 2) {
-                    Object obj = nodeAt(e);
                     if (obj instanceof ChannelNode && !Spacers.isSpacer(((ChannelNode) obj).name)) {
                         actions.joinChannel(((ChannelNode) obj).id);
                     }
+                } else if (SwingUtilities.isMiddleMouseButton(e) && obj instanceof ClientEntry) {
+                    actions.showConnectionInfo((ClientEntry) obj);
                 }
             }
         });