fix(socials): the bar disappeared from the preview when the plate was off

My own regression from the previous commit: the plate Border WRAPPED the bar's content and its
Visibility was bound to BarBackgroundEnabled — so with the plate off (the default) the preview
collapsed the entire social bar. Nothing was wrong with the data; the element was there and
invisible.

Fix: the wrapper is always laid out. "Plate off" now means a TRANSPARENT background
(`SocialBarBackgroundBrush` returns Transparent when disabled) and zero padding, "on" means the
colour/opacity plate with 18,6 padding — which also matches what the renderer bakes for the
output, so preview and broadcast agree.

Guard (new fact in SocialBarAppearanceTests): the preview must never visibility-gate the bar on
BarBackgroundEnabled, the wrapper must bind SocialBarBackgroundBrush, and the plate's switching
must be Padding.

Controls/PreviewPane.xaml

@@ -351,10 +351,18 @@
                                             <DropShadowEffect Color="{Binding SocialBarGlowBrush.Color}"
                                                               BlurRadius="18" ShadowDepth="0" Opacity="0.9"/>
                                         </Grid.Effect>
-                                        <Border HorizontalAlignment="Center" Margin="40,8"
-                                                CornerRadius="20" Padding="18,6"
-                                                Background="{Binding SocialBarBackgroundBrush}"
-                                                Visibility="{Binding Socials.BarBackgroundEnabled, Converter={StaticResource BoolToVis}}">
+                                        <Border HorizontalAlignment="Center" Margin="40,8" CornerRadius="20"
+                                                Background="{Binding SocialBarBackgroundBrush}">
+                                            <Border.Style>
+                                                <Style TargetType="Border">
+                                                    <Setter Property="Padding" Value="0"/>
+                                                    <Style.Triggers>
+                                                        <DataTrigger Binding="{Binding Socials.BarBackgroundEnabled}" Value="True">
+                                                            <Setter Property="Padding" Value="18,6"/>
+                                                        </DataTrigger>
+                                                    </Style.Triggers>
+                                                </Style>
+                                            </Border.Style>
                                         <ItemsControl ItemsSource="{Binding Socials.Entries}"
                                                       HorizontalAlignment="Center"
                                                       IsHitTestVisible="False">

ViewModels/MainViewModel.Socials.cs

@@ -35,8 +35,11 @@ public partial class MainViewModel
     /// so the two cannot drift apart (creator request 2026-10-30).</summary>
     public SolidColorBrush SocialBarTextBrush => SocialBarStyle.From(_socials).TextBrush;
 
-    /// <summary>The preview's plate: same colour AND same opacity the renderer bakes in.</summary>
-    public SolidColorBrush SocialBarBackgroundBrush => SocialBarStyle.From(_socials).BackgroundBrush;
+    /// <summary>The preview's plate: same colour AND same opacity the renderer bakes in.
+    /// Transparent when the plate is off — "off" means no plate, never no bar.</summary>
+    public SolidColorBrush SocialBarBackgroundBrush => _socials?.BarBackgroundEnabled == true
+        ? SocialBarStyle.From(_socials).BackgroundBrush
+        : Brushes.Transparent;
 
     /// <summary>The global socials config (entries + bar settings), or null.</summary>
     public SocialsConfig? Socials => _socials;

ytLive.Tests/SocialBarAppearanceTests.cs

@@ -65,6 +65,20 @@ public class SocialBarAppearanceTests
         Assert.Null(failure);
     }
 
+    [Fact]
+    public void The_preview_bar_is_never_hidden_by_the_plate_switch()
+    {
+        // Regression, 2026-10-30: the plate Border wrapped the whole bar and its Visibility was
+        // bound to BarBackgroundEnabled, so turning the plate off (the default) removed the bar
+        // from the preview entirely. "Plate off" must mean a transparent plate.
+        var preview = SourceAssert.Text("Controls", "PreviewPane.xaml");
+        Assert.DoesNotContain("Socials.BarBackgroundEnabled, Converter={StaticResource BoolToVis}", preview);
+        Assert.Contains("{Binding SocialBarBackgroundBrush}", preview);
+
+        // The plate's PADDING is what switches with the toggle, not the element's presence.
+        Assert.Contains("<Setter Property=\"Padding\" Value=\"18,6\"/>", preview);
+    }
+
     private static VideoFrame? Render(SocialBarStyle style) => SocialBarRenderer.Render(Entries, style);
 
     private static int Count(VideoFrame frame, Func<int, int, int, int, bool> predicate)