A YouTube link that hits "Sign in to confirm you're not a bot" showed
yt-dlp's raw advice to pass --cookies-from-browser or --cookies, which are
CLI flags nobody using VoiceStudio can pass. It now has its own failure
class, VIDEO_DOWNLOAD_BOT_CHECK. Its hint says to export signed-in cookies
as a cookies.txt file and attach it in Dub, or to upload the video
instead. The class is terminal, so it is neither retried as a network drop
nor escalated through player clients like a 403.
Fixes#2034