feat(ui): route locked tiers through About

Keep non-owner resolution choices visible but muted. Selecting one preserves the free tier and opens About; external navigation is only the explicit llamacasty.com link. Ref: https://streamlabs.com/desktop

MainWindow.xaml

@@ -138,8 +138,10 @@
                                Foreground="{StaticResource Brush.Attention}" FontSize="12" TextWrapping="Wrap" Margin="0,0,0,6"/>
 
                     <ComboBox Grid.Row="5" Grid.ColumnSpan="2" VerticalAlignment="Bottom" Style="{StaticResource YtComboBox}"
+                              x:Name="QualityPicker"
                               ItemsSource="{Binding QualityOptions}"
                               SelectedItem="{Binding SelectedQuality}"
+                              ItemContainerStyle="{StaticResource YtQualityComboBoxItem}"
                               DisplayMemberPath="Label"
                               ToolTip="{Binding ResolutionHelp}"
                               IsEnabled="{Binding IsOffline}"/>
@@ -165,7 +167,7 @@
 
 
         <!-- ═══ OVERLAY: Settings / Bug / Feature / About ═══ -->
-        <controls:OverlayHost Grid.RowSpan="3"/>
+        <controls:OverlayHost x:Name="AboutOverlay" Grid.RowSpan="3"/>
 
         <!-- ═══ TOASTS: non-blocking notifications (bottom-right, above footer) ═══ -->
         <notifications:NotificationArea x:Name="ToastArea"