fix: 60s cache TTL on papers PDFs in lith Caddyfile
Added Cache-Control header for *.pdf on papers.aesthetic.computer: max-age=60, must-revalidate. Prevents Cloudflare and browsers from serving stale PDFs after oven rebuilds. Caddy needs to be reloaded on the lith server for this to take effect.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>