feat(ui): coloured dots for icon-less lists, guide line under chevron

Lists without an icon show a dot in a stable identity colour (same
palette/hash as Mission Control tiles); "Dot" is the new picker default.

src/ClaudeDo.Ui/Views/Islands/ListsIslandView.axaml

@@ -73,9 +73,12 @@
             </Border>
             <!-- Icon (list-settings → Icon tab; "Folder" when unset) -->
             <PathIcon Grid.Column="1" Classes="list-icon"
-                      Width="14" Height="14"
+                      Width="14" Height="14" IsVisible="{Binding !IsDot}"
                       Data="{Binding IconKey, Converter={StaticResource IconKey}}"
                       HorizontalAlignment="Center" VerticalAlignment="Center"/>
+            <Ellipse Grid.Column="1" Width="8" Height="8" IsVisible="{Binding IsDot}"
+                     Fill="{Binding DotColorKey, Converter={StaticResource DotBrush}}"
+                     HorizontalAlignment="Center" VerticalAlignment="Center"/>
             <!-- Name -->
             <TextBlock Grid.Column="2" Classes="list-label"
                        Text="{Binding Name}" ToolTip.Tip="{Binding Name}"
@@ -141,10 +144,9 @@
             </Grid>
           </Border>
 
-          <!-- Guide line drops from under the folder icon's centre (padding 10 + chevron 12 + half
-               of the 20px icon slot); children indent one icon slot past it. -->
+          <!-- Guide line drops from under the chevron's centre (padding 10 + half the 9px glyph). -->
           <Panel IsVisible="{Binding !IsCollapsed}">
-            <Border Width="1" HorizontalAlignment="Left" Margin="31,0,0,4"
+            <Border Width="1" HorizontalAlignment="Left" Margin="14,0,0,4"
                     Background="{DynamicResource LineBrush}" IsHitTestVisible="False"/>
             <ItemsControl ItemsSource="{Binding Children}" Margin="20,0,0,0"/>
           </Panel>