root cause of duplicate pipeline entries: rescan.ts flipped done plans
back to pending whenever a post-job jellyfin refresh returned stale
metadata, putting the item back in review and letting a second jobs row
pile up in done. done is now sticky across rescans (error still
re-opens for retries).
second line of defense: before spawning ffmpeg, ffprobe the file and
compare audio count/language/codec order + embedded subtitle count
against the plan. if it already matches, mark the job done with the
reason in jobs.output and skip the spawn. prevents corrupting a
post-processed file with a stale stream-index command.
