feat: implement 1B domain entities/repos + 1H library API routes

1B — domain layer:
- New entities: Album, Playlist, Like, PlayHistoryEntry
- Track entity extended with album_id, genre, year fields
- New protocols: AlbumRepository, PlaylistRepository, LikeRepository, HistoryRepository
- ArtistRepository / TrackRepository protocols extended (list, count, update, get_many, etc.)
- New repos: SqlAlchemyAlbum/Playlist/Like/HistoryRepository
- Artist and track repos updated to match extended protocols

1H — library API:
- Pagination: PagedResponse[T] generic, offset-based, limit default 50 max 200
- Schemas: TrackOut, AlbumOut, ArtistOut, PlaylistOut/Create/Update,
  LikeEvent/State, HistoryIn/Out, LibrarySearchResponse
- GET/PATCH/DELETE /tracks with filters, sort, pagination
- GET /albums, /albums/{id}, /albums/{id}/tracks
- GET /artists, /artists/{id}, /artists/{id}/albums, /artists/{id}/tracks
- GET /search/library (ILIKE across tracks/albums/artists)
- Full /playlists CRUD + track add/remove (append-only version bump)
- POST /likes (append-only event log), GET /likes, GET /likes/state
- POST /history (scrobble), GET /history
- deps.py: TrackRepoDep, ArtistRepoDep, AlbumRepoDep, PlaylistRepoDep,
  LikeRepoDep, HistoryRepoDep

ruff ✅  mypy ✅  pytest 45/45 ✅

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/domain/entities/__init__.py

@@ -1,7 +1,21 @@
 """Domain entities and value objects — pure, framework-free."""
 
+from app.domain.entities.album import Album
+from app.domain.entities.history import PlayHistoryEntry
+from app.domain.entities.like import Like
+from app.domain.entities.playlist import Playlist
 from app.domain.entities.storage import ObjectStat
 from app.domain.entities.track import Artist, Track
 from app.domain.entities.user import Credentials, User
 
-__all__ = ["Artist", "Credentials", "ObjectStat", "Track", "User"]
+__all__ = [
+    "Album",
+    "Artist",
+    "Credentials",
+    "Like",
+    "ObjectStat",
+    "PlayHistoryEntry",
+    "Playlist",
+    "Track",
+    "User",
+]