test: cover list folders in the data and sidebar layers

Data: folder delete keeps its lists (ON DELETE SET NULL), rename patches
name/icon without resetting sort order or collapse state.
Sidebar: grouping on load, folder badge as the sum of its children, both
move routes, and the persisted collapse state.

Drops the LoadAsync/AddRowAsync normalization of a dangling folder_id:
FK enforcement is on for every connection, so the row it guarded against
cannot exist, and ContainerOf already falls back to the top level.

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

@@ -338,9 +338,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
                     IsManual = l.IsManual,
                     FindingsTracked = l.FindingsTracked,
                     HasTicketProject = ticketsConfigured && cfg?.TicketProjectId > 0,
-                    // A folder_id pointing at a folder that isn't there (shouldn't happen — the FK
-                    // sets it null on delete) would otherwise hide the list entirely.
-                    FolderId = Folders.Any(f => f.Id == l.FolderId) ? l.FolderId : null,
+                    FolderId = l.FolderId,
                 };
                 Items.Add(item);
                 UserLists.Add(item);
@@ -707,7 +705,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
             IsManual = entity.IsManual,
             FindingsTracked = entity.FindingsTracked,
             HasTicketProject = hasTicketProject,
-            FolderId = Folders.Any(f => f.Id == entity.FolderId) ? entity.FolderId : null,
+            FolderId = entity.FolderId,
         };
 
         var seedNames = new HashSet<string>(new[] { "My Day", "Important", "Planned" });