creator feedback batch: 9 fixes from initial review

1. About box bg → #0A0C1A (matches icon bg)
2. Elements panel collapses when no element selected / scene changes
3. OpacityChip moved from preview overlay into Elements panel
4. Color picker fix: cast to SceneElement not Source (WebcamSceneConfig was silently blocked)
5. Red left accent bar on selected items in Scene/Source lists
6. ✓ character replaced with Path checkmark icon in Elements panel
7. Removed ToolTip='Applied' from green check buttons
8. Created bugs.md with first entry (iTunes audio on mic meter)
9. Full logo in README + About box uses ytLlive-logo.png

Themes/Controls.xaml

@@ -519,17 +519,23 @@
         <Setter Property="Template">
             <Setter.Value>
                 <ControlTemplate TargetType="ListBoxItem">
-                    <Border x:Name="Bd" Background="{TemplateBinding Background}"
-                            CornerRadius="3" Padding="{TemplateBinding Padding}" Margin="0,1">
-                        <ContentPresenter VerticalAlignment="Center"
-                                          HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"/>
-                    </Border>
+                    <Grid>
+                        <Border x:Name="Accent" Width="3" HorizontalAlignment="Left" CornerRadius="1"
+                                Background="#e94560" Margin="0,2" Opacity="0"
+                                VerticalAlignment="Stretch"/>
+                        <Border x:Name="Bd" Background="{TemplateBinding Background}"
+                                CornerRadius="3" Padding="{TemplateBinding Padding}" Margin="0,1">
+                            <ContentPresenter VerticalAlignment="Center"
+                                              HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"/>
+                        </Border>
+                    </Grid>
                     <ControlTemplate.Triggers>
                         <Trigger Property="IsMouseOver" Value="True">
                             <Setter TargetName="Bd" Property="Background" Value="#22ffffff"/>
                         </Trigger>
                         <Trigger Property="IsSelected" Value="True">
                             <Setter TargetName="Bd" Property="Background" Value="#1a3a66"/>
+                            <Setter TargetName="Accent" Property="Opacity" Value="1"/>
                         </Trigger>
                     </ControlTemplate.Triggers>
                 </ControlTemplate>