.top-bar was unconditionally hidden on every page (admin_chrome library)
on the assumption it always renders empty, which held on our own pages
but not on entity edit forms, where Gin puts the page's local actions --
Save included -- inside .top-bar. Folded it into the same route-scoped
library as the admin sidebar (renamed hide_admin_sidebar ->
hide_admin_chrome) so both are hidden only on our front-end routes and
real admin pages keep a working Save button.
