Crawl policy — controlled by site_indexable, not site_live.

Lets us soft-launch (site_live=1 + site_indexable=0) without search engines catching wind before the public announcement. Flip site_indexable=1 only on launch day.

Cache-Control is deliberately short (5 min) so that toggling site_indexable propagates to search engines within minutes rather than the 4-hour default Cloudflare edge cache. When the site is live-and-indexed this stays at max-age=300; we could bump it once the state is fully stable post-launch.