Top bar and scene strip: EDIT toggle beside REC (orange on, blue off); fixed-size centered mini screens; fixed 360px left column so the empty cell matches the layers panel

- TopBar: EDIT ToggleButton, spaced from the REC/ON-AIR segments
- MainViewModel: explicit EditingActive drives IsEditMode; YouTube go-live turns edit off, stop turns it on
- SceneThumbnailStrip: tiles fixed 196x130 and centered; dark background fills the column so its edge does not move on resize; strip row fixed 154px
- MainWindow: left column fixed at 360px; WIDTHS diagnostic log on resize

Not pushed.

Controls/SceneThumbnailStrip.xaml.cs

@@ -8,12 +8,9 @@ namespace ytLive.Controls;
 
 public partial class SceneThumbnailStrip : UserControl
 {
-    private const double DesignAspect = 154.0 / 1000.0;
-
     public SceneThumbnailStrip()
     {
         InitializeComponent();
-        SizeChanged += (_, _) => Height = ActualWidth * DesignAspect;
         Loaded += (_, _) =>
         {
             if (DataContext is MainViewModel vm)