creator feedback batch: 9 fixes from initial review

1. About box bg → #0A0C1A (matches icon bg)
2. Elements panel collapses when no element selected / scene changes
3. OpacityChip moved from preview overlay into Elements panel
4. Color picker fix: cast to SceneElement not Source (WebcamSceneConfig was silently blocked)
5. Red left accent bar on selected items in Scene/Source lists
6. ✓ character replaced with Path checkmark icon in Elements panel
7. Removed ToolTip='Applied' from green check buttons
8. Created bugs.md with first entry (iTunes audio on mic meter)
9. Full logo in README + About box uses ytLlive-logo.png

MainWindow.xaml.cs

@@ -209,7 +209,7 @@ public partial class MainWindow : Window
         if (e.OriginalSource is not DependencyObject original) return;
         if (IsDescendantOf(original, PreviewGrid)) return;
         if (IsDescendantOf(original, SourceList)) return;
-        if (IsDescendantOf(original, OpacityChip)) return;
+        if (IsDescendantOf(original, ElementsPanel)) return;
         _viewModel.SelectedElement = null;
     }
 
@@ -224,7 +224,6 @@ public partial class MainWindow : Window
     {
         var selected = _viewModel.SelectedElement is { } s && IsDraggableElement(s);
         SelectionOverlay.Visibility = selected ? Visibility.Visible : Visibility.Collapsed;
-        OpacityChip.Visibility = selected ? Visibility.Visible : Visibility.Collapsed;
         if (selected)
             OpacityValueText.Text = $"{Math.Round(_viewModel.SelectedElement!.Opacity * 100)}%";
         TakeSnapshot();
@@ -232,7 +231,7 @@ public partial class MainWindow : Window
 
     // Static images and the webcam share the move/resize/selection behavior.
     private static bool IsDraggableElement(SceneElement element)
-        => element is Source { Type: SourceType.Image } or WebcamSceneConfig;
+        => element.IsDraggable;
 
     private void MirrorButton_Click(object sender, RoutedEventArgs e)
     {
@@ -304,8 +303,6 @@ public partial class MainWindow : Window
 
     private void Preview_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
     {
-        if (OpacityChip.IsMouseOver) return;
-
         var grid = (Grid)sender;
         var toCanvas = CanvasGrid.TransformToVisual(grid).Inverse;
         var p = toCanvas.Transform(e.GetPosition(grid));
@@ -538,7 +535,7 @@ public partial class MainWindow : Window
 
     private void WebcamBorderColorPicker_Click(object sender, RoutedEventArgs e)
     {
-        if (_viewModel.SelectedElement is not Models.Source src) return;
+        if (_viewModel.SelectedElement is not SceneElement src) return;
         if (sender is FrameworkElement fe && fe.ContextMenu == null)
         {
             var menu = new System.Windows.Controls.ContextMenu();