Audit caught two missing providers from the foundation pr. Both
return album-shaped data via their clients (search + download
flows). Tidal uses tidalapi objects rather than dicts so the
converter is from_tidal_object, not _dict.
Enrichment-only providers (lastfm/genius/acoustid/listenbrainz/
audiodb) intentionally have no album converter — they enrich
existing rows, never return album shapes.
Tests: +8 cases. 40 total now.
New core/metadata/types.py with canonical dataclasses + classmethod
converters for spotify/itunes/deezer/discogs/musicbrainz/hydrabase.
Each converter is the single place that knows that provider's wire
shape — addresses the duck-typing pattern Cin flagged.
Pure additive: no consumer code changed. Follow-up PRs migrate
consumers one at a time. Migration plan at
docs/metadata-types-migration.md.
Tests: 32 cases pin per-provider semantics + cross-provider
invariants. Also stabilized a flaky discogs test that depended on
local config state.
