- Root context menu now has tabindex/focus + Escape-key close (OnRootMenuKeyDown) mirroring the node menu
- Opening root menu calls _tree.DismissNodeContextMenu(); opening node menu fires OnNodeContextMenuOpened → DismissRootContextMenu so only one menu is ever visible
- Add FolderContextMenu_MoveUp_IsDisabled_OnFirstSibling and FolderContextMenu_MoveDown_IsDisabled_OnLastSibling bUnit tests