Epic 2: Public pages - layout, theme, home, CV, projects, SEO

The public face: root layout with the token-driven light/dark theme, home with streamed widget loads, CV with a print stylesheet, projects index and detail, changelog, 404, and the SEO plumbing (link previews, sitemap, structured data).

Done when Lighthouse is 95+ on / and /cv and unpublished content is unreachable.