Scene strip: move top row over the preview column and scale it; remove CRT bezel art and on-air seed

- PreviewPane.xaml: drop the OBS-style border Rectangle/Ellipse over webcam elements
- SceneThumbnailStrip: Viewbox scales the row; height follows width so it fills the preview column; staged+live tile has no border
- MainWindow.xaml: strip moved to column 1 only, leaving the layers cell empty; Margin 8,0 matches the preview
- MainViewModel.Background: stop seeding the CRT scene tiles and the on-air image
- ytLive.csproj: per-build counter (BuildCounter.txt, gitignored) replaces the commit-count stamp

Build stamp now increments on every build.

Controls/SceneThumbnailStrip.xaml

@@ -1,7 +1,8 @@
 <UserControl x:Class="ytLive.Controls.SceneThumbnailStrip"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
-    <Border Background="#0d1117" CornerRadius="4" Margin="0,0,0,4" Padding="4">
+    <Viewbox Stretch="Uniform">
+    <Border Width="1000" Height="150" Background="#0d1117" CornerRadius="4" Margin="0,0,0,4" Padding="4">
         <ItemsControl ItemsSource="{Binding Scenes}">
             <ItemsControl.ItemsPanel>
                 <ItemsPanelTemplate>
@@ -25,6 +26,13 @@
                                     <DataTrigger Binding="{Binding IsLive}" Value="True">
                                         <Setter Property="BorderBrush" Value="#22c55e"/>
                                     </DataTrigger>
+                                    <MultiDataTrigger>
+                                        <MultiDataTrigger.Conditions>
+                                            <Condition Binding="{Binding IsStaged}" Value="True"/>
+                                            <Condition Binding="{Binding IsLive}" Value="True"/>
+                                        </MultiDataTrigger.Conditions>
+                                        <Setter Property="BorderBrush" Value="Transparent"/>
+                                    </MultiDataTrigger>
                                 </Style.Triggers>
                             </Style>
                         </Border.Style>
@@ -51,4 +59,5 @@
             </ItemsControl.ItemTemplate>
         </ItemsControl>
     </Border>
+    </Viewbox>
 </UserControl>