New algorithm: pick first track alphabetically from artist's library, search
both Deezer and iTunes APIs for 'artist track' to find the exact artist,
verify name matches, then use max(deezer_id, itunes_id) as the canonical
differentiator. Deterministic across instances — any SoulSync with the same
artist and at least one matching track will produce the same soul_id.
Fallback chain: canonical API ID → first album title → name only.
Migration clears all artist soul_ids on first v2.1 startup for regeneration.