feat(api): finish Group A stubbed endpoints

Implements previously-stubbed /api/v1 endpoints (hexagonal: ports -> repos
-> services -> routers wired in deps):

- playlists: GET /{id}/cover (serves stored cover, 404 when absent)
- settings: GET/PATCH /settings + GET/PUT /settings/scrobbling — lazy
  per-user row, write-only Fernet-encrypted scrobble session key; adds
  user_settings table + migration (chains off dc126696f5a6)
- storage: GET /duplicates, /broken, /missing-metadata + admin POST
  /cleanup (arq cleanup_storage worker; reconciles local refs only,
  guarded against a storage-outage mass delete)
- admin: GET /services, /sources, /settings + POST /reindex; PATCH
  /settings and /sources/{source} return 501 (config is env-managed)

Adds NotSupportedError (-> HTTP 501). Integration tests for each surface.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/domain/entities/settings.py

@@ -0,0 +1,34 @@
+"""User settings domain entity (general preferences + scrobbling config)."""
+
+import uuid
+from dataclasses import dataclass
+
+# Defaults for a user who has never saved settings — the row is created lazily,
+# so reads return these before the first write.
+DEFAULT_THEME = "system"
+DEFAULT_STREAM_QUALITY = "original"
+
+
+@dataclass(frozen=True, slots=True)
+class UserSettings:
+    user_id: uuid.UUID
+    theme: str
+    stream_quality: str
+    scrobble_enabled: bool
+    scrobble_provider: str | None
+    scrobble_username: str | None
+    # Scrobbler session key / user token, encrypted at rest (never leaves the
+    # server in plaintext). ``None`` until the user configures scrobbling.
+    scrobble_session_key_enc: str | None
+
+    @classmethod
+    def defaults(cls, user_id: uuid.UUID) -> UserSettings:
+        return cls(
+            user_id=user_id,
+            theme=DEFAULT_THEME,
+            stream_quality=DEFAULT_STREAM_QUALITY,
+            scrobble_enabled=False,
+            scrobble_provider=None,
+            scrobble_username=None,
+            scrobble_session_key_enc=None,
+        )

app/domain/errors.py

@@ -54,6 +54,13 @@ class PermissionDeniedError(DomainError):
     code = "permission_denied"
 
 
+class NotSupportedError(DomainError):
+    """Operation is intentionally unsupported (e.g. a config knob that is managed
+    via environment, not mutable at runtime)."""
+
+    code = "not_supported"
+
+
 class DependencyUnavailableError(DomainError):
     """An external dependency (source, ML, MusicBrainz) is unavailable.
 

app/domain/ports.py

@@ -29,6 +29,7 @@ from app.domain.entities import (
     SubsonicCredentials,
     User,
 )
+from app.domain.entities.settings import UserSettings
 from app.domain.entities.track import Artist, Track
 from app.domain.sources import DownloadResult, RawMetadata, SearchResult, SourceFile, SourceInfo
 from app.domain.tokens import IssuedToken, TokenClaims, TokenType
@@ -56,6 +57,11 @@ class UserRepository(Protocol):
     async def set_subsonic_password_enc(self, user_id: uuid.UUID, password_enc: str) -> None: ...
 
 
+class UserSettingsRepository(Protocol):
+    async def get(self, user_id: uuid.UUID) -> UserSettings | None: ...
+    async def upsert(self, settings: UserSettings) -> UserSettings: ...
+
+
 class SubsonicCipher(Protocol):
     """Symmetric encrypt/decrypt for the recoverable Subsonic app-password."""
 
@@ -164,6 +170,12 @@ class TrackRepository(Protocol):
     # AlbumRepository below).
     async def genres(self) -> list[tuple[str, int]]: ...
     async def library_stats(self) -> LibraryStats: ...
+    async def find_duplicate_groups(self) -> list[tuple[str, list[Track]]]: ...
+    async def list_by_metadata_status(
+        self, status: str, *, limit: int, offset: int
+    ) -> list[Track]: ...
+    async def all_storage_refs(self) -> list[tuple[uuid.UUID, str]]: ...
+    async def count_by_metadata_status(self, status: str) -> int: ...
     async def list(
         self,
         *,
@@ -287,6 +299,7 @@ class PlaylistRepository(Protocol):
     async def reorder_tracks(
         self, playlist_id: uuid.UUID, ordered_track_ids: list[uuid.UUID]
     ) -> None: ...
+    async def get_cover_path(self, playlist_id: uuid.UUID) -> str | None: ...
     # list must come after any method using list[...] in its signature (name shadowing)
     async def list(self, *, owner_id: uuid.UUID, limit: int, offset: int) -> list[Playlist]: ...