feat(ui): Listen und Ordner in einer gemischten Sidebar-Reihenfolge

Die oberste Sidebar-Ebene ist jetzt eine gemischte TopLevel-Collection, so
dass eine Liste auch oberhalb eines Ordners stehen kann. DropAsync deckt
alle vier Quelle/Ziel-Kombinationen ab, ReorderSidebarAsync numeriert die
gesamte sichtbare Reihenfolge ueber lists und list_folders hinweg.

tests/ClaudeDo.Data.Tests/ListFolderTests.cs

@@ -102,6 +102,36 @@ public sealed class ListFolderTests : IDisposable
             Assert.Null((await ctx.Lists.AsNoTracking().FirstAsync(l => l.Id == "l1")).FolderId);
     }
 
+    [Fact]
+    public async Task ReorderSidebarAsync_numbers_folders_and_lists_in_one_sequence()
+    {
+        await using var ctx = Open();
+        var repo = new ListRepository(ctx);
+        await repo.AddFolderAsync(NewFolder("f1"));
+        await repo.AddAsync(new ListEntity { Id = "inside", Name = "Inside", CreatedAt = DateTime.UtcNow, FolderId = "f1" });
+        await repo.AddAsync(new ListEntity { Id = "top", Name = "Top", CreatedAt = DateTime.UtcNow });
+
+        // Sidebar: the top-level list above the folder, whose one child follows the folder.
+        await repo.ReorderSidebarAsync([("top", false), ("f1", true), ("inside", false)]);
+
+        Assert.Equal(0, (await repo.GetByIdAsync("top"))!.SortOrder);
+        Assert.Equal(1, (await repo.GetFoldersAsync()).Single().SortOrder);
+        Assert.Equal(2, (await repo.GetByIdAsync("inside"))!.SortOrder);
+    }
+
+    [Fact]
+    public async Task AddAsync_appends_past_the_folders_too()
+    {
+        await using var ctx = Open();
+        var repo = new ListRepository(ctx);
+        await repo.AddFolderAsync(NewFolder("f1"));
+        await repo.AddFolderAsync(NewFolder("f2"));
+        await repo.AddAsync(new ListEntity { Id = "l1", Name = "Fresh", CreatedAt = DateTime.UtcNow });
+
+        // 2, not 0 — a new list must not jump above the existing folders on the next load.
+        Assert.Equal(2, (await repo.GetByIdAsync("l1"))!.SortOrder);
+    }
+
     [Fact]
     public async Task AddFolderAsync_appends_in_creation_order()
     {