Replace @astrojs/sitemap with prerendered sitemap endpoint
- Remove @astrojs/sitemap integration
- Add prerendered sitemap.xml.ts endpoint (generates static sitemap at build time)
- Update robots.txt to reference sitemap.xml
- Follows sitemaps.org protocol and Cloudflare best practices
- Auto-updates lastmod date on each build
Co-authored-by: Cursor <cursoragent@cursor.com>