Database hardening
- Standardized lifecycle semantics for future schema work:
- deleted_at for logical deletion / erasure / anonymization lifecycle.
- archived_at for reversible operational archive visibility.
- closed_at and completed_at for workflow terminal timestamps only.
- Attached live inventory evidence for current soft-delete/archive columns, counts, and index coverage.
- Documented follow-ups around
conversations.status = 'archived'compatibility and product-query filters.