Store a SHA-256 of each playlist's name + ordered video ids as last synced from /
pushed to YouTube (migration 0013, backfilled for already-clean linked playlists).
'dirty' is now recomputed on every edit by comparing the current fingerprint to that
baseline instead of being stickily set true. So manually restoring the original order
(or undo back to it) clears dirty on its own — the Reset to YouTube button disappears
and no YouTube read is needed. Baseline is set on read-sync, repull (reset), and a
clean push; a missing baseline counts as dirty (unknown YT state). Verified the
migration's fingerprint matches the app's runtime fingerprint exactly.
