Backend: Add immutable event store for credit lifecycle (append-only domain_events)

[greatest0fallt1me]

Description

Persist all credit lifecycle domain events (opened, draw requested/confirmed, repay confirmed, defaulted, suspended) in an append-only domain_events table to support replay, reconciliation, and audits.

Requirements and context

• Must be secure, tested, and documented.
• Must include idempotency keys / unique constraints to prevent duplicates.

Suggested execution

git checkout -b feature/domain-events-store

Implement changes

• Add domain_events table with type, payload json, aggregate id, created_at.
• Write events from service layer (transactionally if using outbox).
• Tests that assert events are recorded for key operations.
• Document replay strategy.

Test and commit

npm test

Example commit message

feat(db): append-only domain event store for credit lifecycle

Guidelines

• Timeframe: 96 hours.