- rename `starred_by_did` column to `did` - rename `repo_at` column to `subject_at` and removed foreign key constraints. - rename `RepoAt` field to `SubjectAt` - remove `Repo` field and split `models.Star` to `RepoStar` and `StringStar` as now there can be two kinds of reverse mappings. Signed-off-by: Seongmin Lee <git@boltless.me>