In `apps/api/prisma/schema.prisma`, the `Frequency` enum is still in use. We need to update it to `DigestFrequency` and perform the necessary migration. This issue was noted during the review of [PR #35](https://github.com/sweetr-dev/sweetr.dev/pull/35) in [this comment](https://github.com/sweetr-dev/sweetr.dev/pull/35#discussion_r1870621328). cc @waltergalvao