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",
+]

app/domain/entities/album.py

@@ -0,0 +1,17 @@
+"""Album domain entity."""
+
+import datetime as dt
+import uuid
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class Album:
+    id: uuid.UUID
+    title: str
+    artist_id: uuid.UUID
+    year: int | None
+    cover_path: str | None
+    musicbrainz_id: str | None
+    created_at: dt.datetime
+    updated_at: dt.datetime

app/domain/entities/history.py

@@ -0,0 +1,15 @@
+"""Play history domain entity — append-only scrobble log entry."""
+
+import datetime as dt
+import uuid
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class PlayHistoryEntry:
+    id: uuid.UUID
+    user_id: uuid.UUID
+    track_id: uuid.UUID
+    played_at: dt.datetime
+    play_duration_seconds: int | None
+    completed: bool

app/domain/entities/like.py

@@ -0,0 +1,14 @@
+"""Like domain entity — append-only event log entry."""
+
+import datetime as dt
+import uuid
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class Like:
+    id: uuid.UUID
+    user_id: uuid.UUID
+    track_id: uuid.UUID
+    value: str  # "like" | "dislike" | "neutral"
+    created_at: dt.datetime

app/domain/entities/playlist.py

@@ -0,0 +1,16 @@
+"""Playlist domain entity."""
+
+import datetime as dt
+import uuid
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class Playlist:
+    id: uuid.UUID
+    name: str
+    description: str | None
+    owner_id: uuid.UUID
+    version: int
+    created_at: dt.datetime
+    updated_at: dt.datetime

app/domain/entities/track.py

@@ -18,12 +18,15 @@ class Track:
     id: uuid.UUID
     title: str
     artist_id: uuid.UUID
+    album_id: uuid.UUID | None
     file_path: str
     file_format: str
     file_size: int
     source: str
     source_id: str
     duration_seconds: int | None
+    genre: str | None
+    year: int | None
     metadata_status: str
     created_at: dt.datetime
     updated_at: dt.datetime