report/apply/digest can now point at any Yandex Music playlist via a
share link instead of only the account's likes. Fetches the playlist's
tracks and artist genres straight into memory (no disk cache, nothing
persisted) and feeds them through the existing build_rows/render_digest/
apply_classification pipeline. apply supports --label to keep a foreign
playlist's tracks in separate genre playlists instead of merging them
into your own. Closes a gap where UnauthorizedError went uncaught anywhere.
