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

Models/WebcamSceneConfig.cs

@@ -12,5 +12,6 @@ public class WebcamSceneConfig : SceneElement
 {
     public string WebcamId { get; init; } = string.Empty;
     public override bool IsWebcam => true;
+    public override bool IsDraggable => true;
     public override ImageSource? DisplaySource => VideoImageSource;
 }