{# Sticky header: the accent strip, the main navbar, and the sub-nav
travel together and pin to the top so per-section nav stays
reachable while scrolling a long page. #}
{# Sub-nav strip. Pages with per-section actions render their pill
nav in the ``subnav`` block; pages without leave it empty and
the main content flows straight up to the main navbar. #}
{% block subnav %}{% endblock %}