Apply dark mode button styles to ConfigWindow

- Add DarkButton and PrimaryButton styles matching MainWindow
- Remove X close button (Cancel/Save buttons close dialog)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

DellMonitorControl/ConfigWindow.xaml.cs

@@ -164,11 +164,6 @@ public partial class ConfigWindow : Window
         Close();
     }
 
-    private void CloseButton_Click(object sender, RoutedEventArgs e)
-    {
-        Close();
-    }
-
     private class PortConfigRow
     {
         public int VcpValue { get; set; }