Fix: update per-site accent + palette on htmx navigation
The accent colour (style#pcms-site-accent) and palette (html[data-palette])
live in the shell <head>, which is not swapped during htmx nav. As a result
an artist inherited the colours of the previous page (e.g. De Kelderband
got the hub's purple instead of its own green). pcmsNav now sends
accent+palette along; the client updates the accent <style> and
data-palette. Applies to all htmx nav (boost + explicit links).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@…>
![(please configure the [header_logo] section in trac.ini)](/chrome/site/your_project_logo.png){kind=logo}
