feat(ui): clear textbox focus on click outside any text box

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ClaudeDo.App/App.axaml.cs

@@ -21,6 +21,8 @@ public partial class App : Application
     {
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
+            FocusClearing.Install();
+
             desktop.MainWindow = new MainWindow
             {
                 DataContext = Services.GetRequiredService<IslandsShellViewModel>(),