Layers panel and scene strip: scene layers header with icons, per-type layer icons, PROGRAM badge and selected/live orange borders, scene name and hotkey overlays, Starting as default scene

- LeftPanel: SCENE LAYERS header with layer count; per-type blue icons; properties header gear; layers list min/max height; properties placeholder; list and properties indent
- SceneThumbnailStrip: names/hotkeys over the tile; PROGRAM badge with blinking red dot on the selected tile; orange border on selected and live tiles; fixed the element border override that hid the style border; reflag tiles on load
- LiveScene is now set on go-live, record start, and live transitions (it was never assigned, so IsLive never fired)
- Startup stages the scene named Starting
- DESIGN.md: color roles (red = YouTube/on-air/record, orange #ff8c3a = attention, amber = game audio/Super Chat)
- Staged live tile uses background art instead of the green LIVE placeholder

Not pushed.

Controls/SceneThumbnailStrip.xaml.cs

@@ -14,6 +14,16 @@ public partial class SceneThumbnailStrip : UserControl
     {
         InitializeComponent();
         SizeChanged += (_, _) => Height = ActualWidth * DesignAspect;
+        Loaded += (_, _) =>
+        {
+            if (DataContext is MainViewModel vm)
+                foreach (var scene in vm.Scenes)
+                {
+                    var staged = scene.IsStaged;
+                    scene.IsStaged = !staged;
+                    scene.IsStaged = staged;
+                }
+        };
     }
 
     private void Thumbnail_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)