Disable CDN caching for HTML, add Quicklink prefetching

- Change Cache-Control from s-maxage=31536000 to max-age=0,must-revalidate
  for all HTML pages and sitemap (fixes stale content after settings change)
- Remove Cloudflare PurgeURLs call since we're not caching HTML at CDN
- Add Quicklink for client-side prefetching on public blog pages
- Make main branch deploy automatic (remove manual trigger)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.woodpecker/build.yaml

@@ -36,7 +36,6 @@ steps:
     image: alpine
     when:
       branch: main
-      event: manual
     commands:
       - apk add --no-cache openssh-client
       - mkdir -p ~/.ssh