Add "Change Description" to the client menu

Offered for our own client as well as others, with TS3's edit icon. The
description is read back from the server before prompting, since the
model only carries one for clients whose info has been looked at.

Note that client_description is not a clientupdate property even for
ourselves — the server only takes it through clientedit — and that our
own change is not echoed back to us, so the local entry is updated here.

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

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

@@ -99,6 +99,9 @@ public final class ServerTreePanel extends JScrollPane {
 
         /** Opens the full server-groups list dialog for a client. */
         void showServerGroupsDialog(ClientEntry client);
+
+        /** Edits a client's description — our own included. */
+        void changeClientDescription(ClientEntry client);
     }
 
     private final DropIndicatorTree tree;