Milestone #160 Opt 2 (era half). A third taste facet alongside artists
+ genre tags: signed weights over decade buckets ("1990s") derived from
albums.release_date, rebuilt daily and scored into the taste match.
- Migration 0045: taste_profile_eras table (mirrors taste_profile_tags)
+ taste_tuning.era_scale column (DEFAULT 0.5).
- Build side (internal/taste): Config.EraScale ([0,1] damper, mirrors
EnrichedTagScale), accumulate folds each play/like's decade at
base*EraScale, persist atomic-replaces the era rows.
- Scorer (internal/recommendation): TasteProfile gains an era term (own
tanh scale + additive 0.15 share so it never weakens the existing
artist/tag signal when a track is undated); candidate queries return
album release_date; decadeOf mirrors the builder helper.
- Tuning lab: era_scale threaded through recsettings + admin API + web
card (auto-renders the new row) + Go/web tests.
Mood facet deferred to #1534 (partial enrichment coverage + needs
candidate-side enriched-tag loading).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
