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/Forms/ConnectDialog.cs

@@ -19,6 +19,7 @@ public partial class ConnectDialog : Form
     public VoiceCatClient? ConnectedClient { get; private set; }
     public uint SelfUserId { get; private set; }
     public string Nickname { get; private set; } = "";
+    public string ServerName { get; private set; } = "";
 
     public ConnectDialog()
     {
@@ -115,6 +116,10 @@ public partial class ConnectDialog : Form
         SetBusy(true);
         lblStatus.Text = "Connecting...";
 
+        ServerName = string.IsNullOrWhiteSpace(server.DisplayName)
+            ? $"{server.Host}:{server.Port}"
+            : server.DisplayName;
+
         string tofuDir = Path.GetDirectoryName(ServerListStore.TofuStorePath)!;
         Console.WriteLine($"[ConnectDialog] tofu store dir: {tofuDir}");
         Directory.CreateDirectory(tofuDir);