Populate the 'To Delete' album

[efimsky]

Depends on: #15

DeletionService creates or reuses an album "PhotoDedupe — To Delete" and adds user-approved target assets via PHAssetCollectionChangeRequest. (Adds to album only — does not delete.)

Acceptance criteria

• Album created once and reused.
• Approved matches appear in the album in Photos.app.
• Adding the same asset twice doesn't duplicate it in the album.