Cleans up the code quality by migrating from Raw SQL to TypeORM
entities. The previous implementation was necessary to do cross‑schema
table joins but since we've migrated to the core schema we don't need it
anymore.
- Also extracted `toIsoStringOrNull` to a utility it was duplicated
several times
- Moved `isThrottled` logic from job handler to cron enqueuer
neo773
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