Subdomain Deploys

Per-collection subdomain support is now available. Set subdomain = "docs" on a collection to deploy it to docs.example.com with its own sitemap, RSS, robots.txt, and search index. Each subdomain collection gets a separate output directory (dist-subdomains/{name}/) and is deployed independently. Supports Cloudflare Pages and Netlify with per-collection deploy_project overrides. The dev server previews subdomain content at /{name}-preview/.