fix: Vary: HX-Request + no-store on partials — no unstyled page on back navigation
The browser cached an htmx partial (only #pcms-main, without <head>/CSS) under
the URL and served it on back/forward as a full page → bare HTML. Vary:
HX-Request separates partial vs full in the cache; no-store on the partial
forces a fresh full-load on back.
Co-Authored-By: Claude <noreply@…>
![(please configure the [header_logo] section in trac.ini)](/chrome/site/your_project_logo.png){kind=logo}
