feat(storage): S3-compatible storage adapter + storage_uri rename

Add S3FileStorage adapter (any S3-compatible backend: AWS, MinIO, Garage)
alongside the local adapter, selected via STORAGE_BACKEND. Proxied range
streaming via get_object+Range; as_local_path downloads to a tempfile for
ffmpeg/fpcalc. Rename track.file_path -> storage_uri across domain entity,
ORM, repositories, port, and services, with an Alembic migration. Adds
mocked S3 unit tests.

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

app/infrastructure/db/repositories/like_repository.py

@@ -30,7 +30,7 @@ def _track_to_entity(row: TrackModel) -> Track:
         title=row.title,
         artist_id=row.artist_id,
         album_id=row.album_id,
-        file_path=row.file_path,
+        storage_uri=row.storage_uri,
         file_format=row.file_format,
         file_size=row.file_size,
         source=row.source,