The preflight system check already warns in-app when yt-dlp is missing
(Voice Gallery/Dub YouTube downloads fail without it), but the install
docs never mentioned it — a user has to hit the in-app warning first
instead of seeing it up front alongside the other optional prereqs.
Co-authored-by: mergetest <test@local>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>