Groundwork for unifying Discover-page playlists (ListenBrainz, Last.fm
radio, SoulSync Discovery) with Sync-page playlists (Spotify, Tidal,
Qobuz, YouTube, Spotify public, iTunes link). All nine sources now
expose the same `PlaylistSource` Protocol so callers stop having to
branch per-source.
This commit only adds the abstraction — no dispatch sites collapse to
the registry yet, no DB or UI changes. Adapters wrap existing clients
via injected getter callables to avoid eager imports of web_server.py
globals.
- core/playlists/sources/base.py — PlaylistMeta, NormalizedTrack,
PlaylistDetail dataclasses + PlaylistSource Protocol with
supports_listing / supports_refresh / requires_auth capability
flags. needs_discovery flag on NormalizedTrack marks tracks that
carry raw MB metadata (LB, Last.fm) vs tracks already matched to a
provider ID (everything else).
- core/playlists/sources/registry.py — thread-safe lazy-factory
registry with instance caching + re-register invalidation.
- nine adapters in core/playlists/sources/ wrapping SpotifyClient,
TidalClient, QobuzClient, spotify_public_scraper, the YouTube +
iTunes-link parsers (via injected callables), ListenBrainzManager,
Last.fm radio rows in the ListenBrainz cache, and
PersonalizedPlaylistManager.
- tests/test_playlist_sources_adapters.py — 18 tests covering each
adapter's field projection with fake backing clients, plus
registry lazy-construct + cache + re-register invalidation.
Phase 1 will collapse refresh_mirrored.py's per-source if/elif chain
to a registry lookup and surface ListenBrainz as a Sync-page tab.
