Genius rate limits are undocumented but users hit 429s at ~40 req/min.
Bumping interval from 1.5s to 2s drops throughput to ~30 req/min which
stays under the threshold. No functional change — just slower enrichment.
The manual match modal for Genius only returned 0 or 1 artist result
because search_artist() searched songs (per_page=5), extracted the
primary artist, and returned the first match or None.
Added search_artists() that returns multiple unique artists extracted
from song results with broader search (per_page=20). The manual match
endpoint now shows up to 8 artist candidates and multiple track results
instead of one-or-nothing. Also shows the Genius URL as extra info.
