Core Navigation's top bar only shows itself when its tools/context/
actions regions are non-empty (`:has(:not(:empty))`). With no blocks
placed in those regions, they still contain whitespace text nodes from
Twig's loop scaffolding, which defeats that check -- the bar rendered
anyway, empty, and pushed page content down to make room for it.
Attached globally via hook_page_attachments() rather than scoped to
/lignes or /dashboard, since the Navigation chrome renders on every
authenticated page, not just our custom routes.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
