Portfolio without downloads; Om mig, Kontakt and Posters come from the portal on the same domain

Linus 2026-11-06: everything public lives on imagesbyolofsson.se (Cleura), the customer
subdomain is only for ordering and the logged-in portal; photos are sold as posters
instead of being downloadable.

- Portfolio: download menu (S/M/L), the original password dialog and /download/original
  are gone; the lightbox has "Köp som poster" -> /posters instead.
- about.astro and contact.astro removed: Caddy on Cleura sends /about, /contact and
  /posters to the portal, so the About text and collaborations are edited once in admin.
  They stay in sitemap-0.xml (PORTAL_PAGES); the sitemap index lists /posters/sitemap.xml.
- Menu and 404 page link Posters; privacy, robots.txt and llms.txt no longer mention
  password downloads.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/layouts/MainLayout.astro

@@ -45,6 +45,7 @@ const ogHeight = Number(og.attributes.height) || undefined;
 
 const nav = [
   { href: '/portfolio', label: 'Portfolio' },
+  { href: '/posters', label: 'Posters' },
   { href: '/tjanster', label: 'Tjänster' },
   { href: '/about', label: 'Om mig' },
   { href: '/contact', label: 'Kontakt' },