feat(library): lazy materialization foundation for remote tracks (§Phase1)

Adds nullable storage fields + availability column on tracks, remote
source/source_id identity on albums/artists, TrackRepository.materialize()
and get_or_create_remote() repos — groundwork for on-demand YTM library
(placeholders saved without audio, materialized in-place on first play).

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

app/infrastructure/db/repositories/track_repository.py

@@ -10,6 +10,7 @@ from app.domain.entities.storage import FormatBreakdown, LibraryStats
 from app.domain.entities.track import Track
 from app.domain.errors import NotFoundError
 from app.infrastructure.db.models.artist import ArtistModel
+from app.infrastructure.db.models.enums import TrackAvailability
 from app.infrastructure.db.models.track import TrackModel
 
 
@@ -31,6 +32,7 @@ def _to_entity(row: TrackModel) -> Track:
         metadata_status=row.metadata_status,
         metadata_error=row.metadata_error,
         enriched_at=row.enriched_at,
+        availability=row.availability,
         created_at=row.created_at,
         updated_at=row.updated_at,
     )
@@ -61,13 +63,14 @@ class SqlAlchemyTrackRepository:
         id: uuid.UUID,
         title: str,
         artist_id: uuid.UUID,
-        storage_uri: str,
-        file_format: str,
-        file_size: int,
+        storage_uri: str | None,
+        file_format: str | None,
+        file_size: int | None,
         source: str,
         source_id: str,
         metadata_status: str,
         added_by: uuid.UUID | None,
+        availability: str = TrackAvailability.LOCAL.value,
     ) -> Track:
         row = TrackModel(
             id=id,
@@ -80,12 +83,38 @@ class SqlAlchemyTrackRepository:
             source_id=source_id,
             metadata_status=metadata_status,
             added_by=added_by,
+            availability=availability,
         )
         self._session.add(row)
         await self._session.flush()
         await self._session.refresh(row)
         return _to_entity(row)
 
+    async def materialize(
+        self,
+        track_id: uuid.UUID,
+        *,
+        storage_uri: str,
+        file_format: str,
+        file_size: int,
+        bitrate: int | None,
+    ) -> Track:
+        """Fill in a remote placeholder's audio fields after a download (lazy
+        materialization). ``track.id`` is unchanged, so likes/playlists/queue
+        entries that already reference it keep working."""
+        row = await self._session.get(TrackModel, track_id)
+        if row is None:
+            raise NotFoundError(f"Track {track_id} not found.")
+        row.storage_uri = storage_uri
+        row.file_format = file_format
+        row.file_size = file_size
+        if bitrate is not None:
+            row.bitrate = bitrate
+        row.availability = TrackAvailability.LOCAL.value
+        await self._session.flush()
+        await self._session.refresh(row)
+        return _to_entity(row)
+
     async def delete(self, track_id: uuid.UUID) -> None:
         row = await self._session.get(TrackModel, track_id)
         if row is not None:
@@ -130,6 +159,7 @@ class SqlAlchemyTrackRepository:
                     func.count(TrackModel.id),
                     func.coalesce(func.sum(TrackModel.file_size), 0),
                 )
+                .where(TrackModel.file_format.is_not(None))
                 .group_by(TrackModel.file_format)
                 .order_by(func.sum(TrackModel.file_size).desc())
             )