Event Sourcing over CRUD for Audit Trails

Decision: Replace standard CRUD in PostgreSQL with Event Sourcing for financial transaction audit trails.

Context: The current CRUD approach overwrites previous states in PostgreSQL. When compliance requested the history of transaction #8821 (who changed status from pending to approved), the team could not provide this information because updates overwrite previous row states.

Alternatives considered:
- Database triggers writing to a history_logs table on every UPDATE: Rejected by Alice (Lead) because business context is lost. A trigger only sees raw row changes (e.g., status changed from 1 to 2) and does not capture why the change happened or the user intent behind it.

Chosen approach:
- Event Sourcing: Store a sequence of immutable domain events (e.g., TransactionCreated, TransactionApproved, StatusUpdated) instead of a mutable current state table.
- Use Kafka to store the immutable event log.
- Build a materialized view in Postgres for fast reads on the frontend.

Reference: Martin Fowler's 'Event Sourcing Pattern' article - industry standard for this pattern.

Implementation plan:
- Event producers: src/services/transactionService.ts (Bob)
- Consumer/store logic: src/events/eventStore.ts
- The architecture satisfies compliance audit requirements while providing fast reads via materialized views.