feat(ui): auto-select first changed file in diff modal

src/ClaudeDo.Ui/ViewModels/Modals/WorktreeModalViewModel.cs

@@ -152,5 +152,18 @@ public sealed partial class WorktreeModalViewModel : ViewModelBase
             if (parent == null) Root.Add(leaf);
             else parent.Children.Add(leaf);
         }
+
+        SelectedNode = FindFirstLeaf(Root);
+    }
+
+    private static WorktreeNodeViewModel? FindFirstLeaf(IEnumerable<WorktreeNodeViewModel> nodes)
+    {
+        foreach (var n in nodes)
+        {
+            if (!n.IsDirectory) return n;
+            var nested = FindFirstLeaf(n.Children);
+            if (nested is not null) return nested;
+        }
+        return null;
     }
 }