The command-item list of a panel context menu. Purely presentational — the
command set is supplied by the parent as plain Callbacks, and
positioning/dismissal/theming belong to the enclosing PortalModal (the
same body-mounted, theme-attributed delivery as the Export/Copy menus).
Sub-menus are CSS-only :hover flyouts nested inside their parent row, so
they live inside the same PortalModal host (focus never leaves it) and
selection routes through the same on_select + on_close path.