Layout example
A different layout can live inside the same PHP base.
This demo uses `app/sections/demo/layouts/immersive.php` and section-local partials. Any subpage can replace the whole shape without touching the main site.
Own layout
A section can bypass the default layout entirely.
Own partials
Header and footer resolve from the section folder first.
Own markup
The page stays plain PHP and can be as custom as needed.