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/ViewModels/Modals/ListSettingsModalViewModel.cs

@@ -111,7 +111,7 @@ public sealed partial class ListSettingsModalViewModel : ViewModelBase
 
     public ObservableCollection<string> CommitTypeOptions { get; } = new(CommitTypeRegistry.Types);
 
-    public const string DefaultIcon = "Text";
+    public const string DefaultIcon = "Dot";
 
     /// <summary>Default icon for folders, kept apart from <see cref="DefaultIcon"/> so lists never look like folders.</summary>
     public const string DefaultFolderIcon = "Folder";
@@ -123,7 +123,7 @@ public sealed partial class ListSettingsModalViewModel : ViewModelBase
     public static readonly string[] IconOptions =
     [
         // general
-        "Folder", "Star", "Sun", "Calendar", "Clock", "Inbox", "Mail", "Text", "Search", "Grid",
+        "Dot", "Folder", "Star", "Sun", "Calendar", "Clock", "Inbox", "Mail", "Text", "Search", "Grid",
         // dev
         "Code", "Terminal", "Database", "Server", "Chip", "Bolt", "Wand", "Flask", "Shield",
         // status / flow