Restructure indexOneArtist to run LB discography fetches and MB
artist image resolution concurrently. They use different rate
limiters (LB: 3 req/s, MB: 1 req/s) so they overlap without
contention.
Per artist, the indexer now runs two parallel pipelines:
LB pipeline: top-release-groups + top-recordings
MB pipeline: url-rels → Wikidata P18 → Wikimedia image fetch
All artist images are pre-cached during the index build instead
of being resolved on-demand during search. Total build time
drops from ~105 min (sequential) to ~63 min (parallel, MB-bound).
SearchIndex now takes ArtistImageProvider as a dependency. The
Service constructor creates artistImg before the index so both
can share it.
yonlu
c9b3c86f37