Set YTDLP_COOKIES_HOST in server/.env and compose mounts the host
cookies.txt read-only at /cookies.txt and wires YTDLP_COOKIES
automatically — no compose edits per host. Falls back to /dev/null when
unset so the container still starts. Add server/.env.example, gitignore
server/.env, and document the flow.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
