Merge Artists

curl --request PUT \
  --url https://server26-dot-royalti-project.uc.r.appspot.com/artist/{id}/merge \
  --header 'Authorization: Bearer <token>'

{
  "message": "Artists merged successfully",
  "assetsUpdatedCount": 5,
  "productsUpdatedCount": 3,
  "artistsDeletedCount": 2,
  "totalChanges": 10
}