The popularity-scaled filter threshold couldn't distinguish 'unknown
popularity' (not in index) from 'confirmed zero' because most
zero-pop artists aren't in the explore index at all. Both cases
got HasPopularity=false.
Simpler approach: remove the special zero-pop filter entirely. With
proper popularity normalization (no +10M contamination), zero-pop
artists get blended scores of ~33-37 and naturally fall below
position 15 in the maxResults cap. Shannon Hale (score 36) ranks
#19 — cut by the cap, no special filtering needed.
Removed minScoreForArtist, minScoreZeroPop, and the HasPopularity/
Popularity-based filtering logic. The minBlendedScore=15 floor
catches extreme edge cases.