fix(windows): polish hotkeys, user list, titlebar, and PM window

- Suppress the system ding on global hotkeys/PTT and the user-list Enter
  key by setting SuppressKeyPress (Handled alone leaves WM_CHAR to beep).
- Preserve the user-list keyboard selection across talking/mute refreshes
  instead of resetting it on every Items.Clear().
- Include the connected server name in the main window titlebar.
- Close the private-message window on Escape.
- Show the PM window without an owner so focus is no longer trapped to it
  and the main window can be worked in while a PM is open.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

clients/windows/VoiceCat.App/Program.cs

@@ -30,7 +30,7 @@ internal static class Program
 
         Console.WriteLine("Launching MainForm...");
         Application.Run(new MainForm(connectDialog.ConnectedClient, connectDialog.SelfUserId,
-            connectDialog.Nickname));
+            connectDialog.Nickname, connectDialog.ServerName));
         Console.WriteLine("MainForm closed. Exiting.");
     }
 }