[nooby6]

Summary

• Accept an optional RFC 3339 available_at timestamp when creating a job.
• Persist the requested availability time, defaulting to the current database time when omitted.
• Keep scheduling enforcement in the existing PostgreSQL claim query, so workers cannot claim jobs before they become available.
• Document the API and add service, repository, and PostgreSQL queue integration coverage.

Validation

• Added tests for request validation and timestamp persistence.
• Added a PostgreSQL integration test proving a scheduled job is not claimable before available_at and becomes claimable afterward.
• GitHub Actions will run the full PostgreSQL-backed test suite.