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/infrastructure/db/repositories/artist_repository.py

@@ -1,10 +1,14 @@
 """Artist repository — adapter over ``AsyncSession``."""
 
-from sqlalchemy import select
+import uuid
+
+from sqlalchemy import func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.domain.entities.track import Artist
+from app.infrastructure.db.models.album import AlbumModel
 from app.infrastructure.db.models.artist import ArtistModel
+from app.infrastructure.db.models.track import TrackModel
 
 
 def _to_entity(row: ArtistModel) -> Artist:
@@ -30,3 +34,49 @@ class SqlAlchemyArtistRepository:
             await self._session.flush()
             await self._session.refresh(row)
         return _to_entity(row)
+
+    async def get_by_id(self, artist_id: uuid.UUID) -> Artist | None:
+        row = await self._session.get(ArtistModel, artist_id)
+        return _to_entity(row) if row is not None else None
+
+    async def get_many(self, ids: list[uuid.UUID]) -> list[Artist]:
+        if not ids:
+            return []
+        rows = (
+            (await self._session.execute(select(ArtistModel).where(ArtistModel.id.in_(ids))))
+            .scalars()
+            .all()
+        )
+        return [_to_entity(r) for r in rows]
+
+    async def list(self, *, q: str | None, limit: int, offset: int) -> list[Artist]:
+        stmt = select(ArtistModel)
+        if q:
+            stmt = stmt.where(ArtistModel.name.ilike(f"%{q}%"))
+        stmt = stmt.order_by(ArtistModel.name).limit(limit).offset(offset)
+        rows = (await self._session.execute(stmt)).scalars().all()
+        return [_to_entity(r) for r in rows]
+
+    async def count(self, *, q: str | None) -> int:
+        stmt = select(func.count()).select_from(ArtistModel)
+        if q:
+            stmt = stmt.where(ArtistModel.name.ilike(f"%{q}%"))
+        return (await self._session.execute(stmt)).scalar_one()
+
+    async def album_count(self, artist_id: uuid.UUID) -> int:
+        return (
+            await self._session.execute(
+                select(func.count())
+                .select_from(AlbumModel)
+                .where(AlbumModel.artist_id == artist_id)
+            )
+        ).scalar_one()
+
+    async def track_count(self, artist_id: uuid.UUID) -> int:
+        return (
+            await self._session.execute(
+                select(func.count())
+                .select_from(TrackModel)
+                .where(TrackModel.artist_id == artist_id)
+            )
+        ).scalar_one()