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

ViewModels/MainViewModel.cs

@@ -213,7 +213,10 @@ public class MainViewModel : ViewModelBase
         set
         {
             if (SetProperty(ref _selectedElement, value))
+            {
                 OnPropertyChanged(nameof(IsWebcamSelected));
+                OnPropertyChanged(nameof(IsElementsPanelEmpty));
+            }
         }
     }
 
@@ -263,6 +266,11 @@ public class MainViewModel : ViewModelBase
     /// <summary>Shows the mirror / clip-shape row in the source chip when a webcam is selected.</summary>
     public bool IsWebcamSelected => SelectedElement is WebcamSceneConfig;
 
+    /// <summary>True when the Elements panel should show the "No configurable elements" hint.</summary>
+    public bool IsElementsPanelEmpty => SelectedElement is { } el
+        && !el.IsDraggable && !el.IsWebcam
+        && el is not Source { Type: SourceType.Countdown or SourceType.WebSource };
+
     /// <summary>
     /// The reason the webcam feed is down (device in use, offline, locked, no frames),
     /// or null when it's alive. Surfaced as a red chip so a dead camera is never a