This page has no shell of its own — just content plus one loader line
(pure-shell.js). Whatever chrome you see around it (admin rail vs. public rail)
is chosen dynamically by the loader based on this page's menu group.
How to test:
1. In Navigation Management, add this page (/pure-shell-demo) to the
admin menu reload it renders inside the admin app shell.
2. Remove it from the admin menu (leave it only in the primary menu) reload it renders inside the public app shell.
The page HTML never changes — only the menu group does. That's the dynamic shell selection.