refactor(enrichment): unify the duplicated/divergent fuzzy-match scorer (one best-match fn)

[thewrz]

Why

Surfaced by the #541 search→queue consistency audit. The same "best fuzzy match" decision is implemented twice, and the copies have drifted:

• app/services/sync/enrichment_pipeline.py::_find_best_match (the request/master-store path) — has a min_artist_score floor (0.35), a BPM-consensus tiebreaker (+0.01), version bonus/penalty (±0.1, min_score 0.4), and structured logging.
• The inline matcher in app/services/recommendation/enrichment.py (enrich_from_beatport / enrich_from_tidal, ~:31/:121) — same core scoring (fuzzy_match_score + artist_match_score + version bonus) but missing the min_artist_score floor, the BPM-consensus tiebreaker, and the logging.

Same decision in 3+ call sites with behavioral drift → meets the DRY-extraction bar. The recommendation copy can accept a worse-artist match the request path would reject.

What

• Extract ONE shared best-match function (e.g. app/services/track_normalizer.py or a small match.py) with the request-path behavior (incl. min_artist_score + BPM-consensus tiebreaker), and route both the enrichment pipeline and the recommendation engine through it.
• This also sets up feat(setbuilder): pool reads global store + pool→builder contract & build coverage gate #542 (pool→master-store), which will want the identical matcher when pool imports funnel into the same tracks row.

Notes / context

• Out of scope for feat(enrichment): write the global track store at request time (enrich once, reuse everywhere) #541 (feat(enrichment): write the master track store at request time — enrich once, reuse everywhere (#541) #550) — that's the request-queue master-store surface; this is the recommendation surface. Filed as a follow-up per the audit.
• Related cross-surface naming drift (musical_key vs key/camelot, bpm int vs float across SearchResult/TrackProfile/BeatportSearchResult) should be reconciled when feat(setbuilder): pool reads global store + pool→builder contract & build coverage gate #542 funnels pool writes into tracks.

Source: #541 search→queue consistency audit (MEDIUM-3).