Baseline: WPF/Avalonia/Cli/Core + plans (BROWSER_FEATURES_PLAN v2, MOBILE_PLAN v1)

VideoDownloader.App/Converters.cs

@@ -0,0 +1,15 @@
+using System.Globalization;
+using System.Windows;
+using System.Windows.Data;
+
+namespace VideoDownloader.App;
+
+/// <summary>컬렉션 카운트 → 빈 상태 표시용 (0일 때 Visible)</summary>
+public class InverseCountToVisibilityConverter : IValueConverter
+{
+    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        => (value is int i && i > 0) ? Visibility.Collapsed : Visibility.Visible;
+
+    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        => throw new NotImplementedException();
+}