- Add CoverAssetId FK and CoverAsset navigation to Album model - Add AlbumAssetPreviewDto with resolution/thumbnail info - Extend AlbumPreviewDto/FullDto with PersonName, CoverAssetId, AssetCount - Add CoverAssetId to AlbumCreateDto and AlbumUpdateDto - Update AlbumMapper to populate new fields from eager-loaded relations - Add EF migration for CoverAssetId column