Add MusicLibrary.Collection.Enrichment module with batch scrobble, artist
country, and selected release enrichment from existing tables.
Wire enrichment into all four collection API endpoints (index, latest,
random, on_this_day). New JSON fields: scrobble_count, last_listened_at,
artist_country, selected_release.
Uses 3 fixed-count batch queries regardless of page size — no N+1 risk.
No schema changes or migrations required.
Use Integer.parse/1 instead of String.to_integer/1 on user-supplied
and external API input to prevent ArgumentError crashes on non-numeric
values. Adds fallback defaults or nil returns at each call site.
Claudio Ortolina