Screen backdrop (schema v5/v6) + five-scene catalog + webcam polish: live desktop/game capture as a permanent non-deletable bottom layer (Source.IsBackdrop), auto full-screen game detection (Win32FullScreenDetector) else primary display, GraphicsCapturePicker re-designation, refcounted shared ScreenCaptureManager, Live-only backdrop by policy (HasBackdrop + v5-v6 backfill + EnforceBackdropPolicy, checkbox gone), SceneCatalog (Starting/Live/BRB/Chat/Ending) with + button re-adding missing scenes, webcam mid-session transparent-container fix (GetPreviewBitmap propagation), Chat half-screen-area cap, 'Add Webcam' always opens the picker (SwapWebcamIdentityAsync, no silent resurrect), WindowsRuntimeMarshal frame-read + 5s-throttled errors, docs updated, tests (65 passing)

Models/Scene.cs

@@ -11,6 +11,7 @@ public class Scene : INotifyPropertyChanged
     private string _name = string.Empty;
     private bool _isEditing;
     private bool _isHidden;
+    private bool _hasBackdrop;
 
     public string Name
     {
@@ -30,6 +31,16 @@ public class Scene : INotifyPropertyChanged
         set => Set(ref _isHidden, value);
     }
 
+    /// <summary>
+    /// Whether the scene has a live desktop/game backdrop layer. Enforced by
+    /// policy: only the canonical Live scene ever has one (see SceneCatalog).
+    /// </summary>
+    public bool HasBackdrop
+    {
+        get => _hasBackdrop;
+        set => Set(ref _hasBackdrop, value);
+    }
+
     /// <summary>
     /// The scene's rendered elements in z-order (back to front): multi-instance
     /// Sources plus this scene's webcam usage (<see cref="WebcamConfig"/>), if any.