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

@@ -1,17 +1,16 @@
 <UserControl x:Class="ytLive.Controls.SceneThumbnailStrip"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
-    <Viewbox Stretch="Uniform">
-    <Border Width="1000" Height="150" Background="#0d1117" CornerRadius="4" Margin="0,0,0,4" Padding="4">
-        <ItemsControl ItemsSource="{Binding Scenes}">
+    <Border Background="#0d1117" CornerRadius="4" Padding="4">
+        <ItemsControl ItemsSource="{Binding Scenes}" HorizontalAlignment="Center" VerticalAlignment="Center">
             <ItemsControl.ItemsPanel>
                 <ItemsPanelTemplate>
-                    <UniformGrid Rows="1" Columns="5"/>
+                    <StackPanel Orientation="Horizontal"/>
                 </ItemsPanelTemplate>
             </ItemsControl.ItemsPanel>
             <ItemsControl.ItemTemplate>
                 <DataTemplate>
-                    <Border CornerRadius="4" Margin="2" Padding="2"
+                    <Border Width="196" Height="130" CornerRadius="4" Margin="2" Padding="2"
                             BorderThickness="2"
                             Cursor="Hand"
                             MouseLeftButtonDown="Thumbnail_MouseLeftButtonDown">
@@ -83,5 +82,4 @@
             </ItemsControl.ItemTemplate>
         </ItemsControl>
     </Border>
-    </Viewbox>
 </UserControl>

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)

Controls/TopBar.xaml

@@ -54,6 +54,21 @@
              reality line + End so nothing mid-session can be re-armed. -->
         <StackPanel Grid.Column="1" Orientation="Horizontal"
                     HorizontalAlignment="Center" VerticalAlignment="Center">
+            <!-- EDIT: explicit toggle. Blue = off (chat), orange = on (layers/properties). -->
+            <ToggleButton IsChecked="{Binding EditingActive, Mode=TwoWay}" Content="EDIT"
+                          Cursor="Hand" Height="32" Padding="14,0" Margin="0,0,24,0" VerticalAlignment="Center"
+                          FontWeight="Bold" FontSize="12" Foreground="#0b1326" BorderThickness="0">
+                <ToggleButton.Style>
+                    <Style TargetType="ToggleButton">
+                        <Setter Property="Background" Value="#38bdf8"/>
+                        <Style.Triggers>
+                            <Trigger Property="IsChecked" Value="True">
+                                <Setter Property="Background" Value="#ff8c3a"/>
+                            </Trigger>
+                        </Style.Triggers>
+                    </Style>
+                </ToggleButton.Style>
+            </ToggleButton>
             <!-- IDLE: the mode switch + the action(s) of the armed world. The three
                  controls share one height (build 77 feedback) so they read as one
                  family — segments host, Start/Go Live, and Test all sit at 32. -->