feat(ui): make sidebar folder hierarchy readable

Lists default to the Text icon instead of the folder icon, rows align
across depths with a guide line per open folder, folder names are
semibold, folder counts only show while collapsed and zero counts hide.

src/ClaudeDo.Ui/ViewModels/Islands/ListsIslandViewModel.cs

@@ -30,6 +30,9 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
     /// <summary>Icon key a folder falls back to when it has none of its own.</summary>
     public const string ListFolderIcon = "Folder";
 
+    /// <summary>Icon key a list falls back to — deliberately not the folder icon, so the two stay distinguishable.</summary>
+    public const string ListIcon = ListSettingsModalViewModel.DefaultIcon;
+
     private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
     private readonly IServiceProvider? _services;
     private readonly IWorkerClient? _worker;
@@ -368,7 +371,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
                     Id = $"user:{l.Id}",
                     Name = l.Name,
                     Kind = ListKind.User,
-                    IconKey = l.Icon ?? "Folder",
+                    IconKey = l.Icon ?? ListIcon,
                     WorkingDir = l.WorkingDir,
                     DefaultCommitType = l.DefaultCommitType,
                     IsManual = l.IsManual,
@@ -473,7 +476,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
             Id = $"user:{entity.Id}",
             Name = entity.Name,
             Kind = ListKind.User,
-            IconKey = "Folder",
+            IconKey = ListIcon,
             WorkingDir = entity.WorkingDir,
             DefaultCommitType = entity.DefaultCommitType,
         };
@@ -840,7 +843,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
             row.DefaultCommitType = entity.DefaultCommitType;
             row.IsManual = entity.IsManual;
             row.FindingsTracked = entity.FindingsTracked;
-            row.IconKey = entity.Icon ?? "Folder";
+            row.IconKey = entity.Icon ?? ListIcon;
             row.HasTicketProject = hasTicketProject;
             RecomputeHasNoLinkedRepo();
         }
@@ -886,7 +889,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
             Id = $"user:{entity.Id}",
             Name = entity.Name,
             Kind = ListKind.User,
-            IconKey = entity.Icon ?? "Folder",
+            IconKey = entity.Icon ?? ListIcon,
             WorkingDir = entity.WorkingDir,
             DefaultCommitType = entity.DefaultCommitType,
             IsManual = entity.IsManual,