CR: Create interactions API for fetching email delivery statues for registrations and applications

### Description

Provide authenticated REST endpoints so Examiner UI can retrieve outbound communication records for an application or registration, including delivery status and per-recipient detail populated by the interactions-update job.

### Acceptance criteria

- Authenticated examiner clients can retrieve interactions for a given application or registration.
- the response includes status and reason for failures
- API responses include aggregate delivery status and per-recipient `deliveries` when the update job has processed the record.
- Unit / Integration tests cover authorization, response shape, and empty-state behaviour.