feat: add audit logging for critical backend actions

.gitignore

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 node_modules
 coverage
 dist
-coverage
 .env
 .env.*
 .DS_Store
 *.log
-coverage
+coverage/

AUDIT_RETENTION.md

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+# Audit Log Retention and Privacy Considerations
+
+## Retention Policy
+Audit logs in the current implementation are stored in-memory using the `InMemoryAuditLogRepository`. 
+- **Volatile Storage**: Since the storage is in-memory, logs are cleared whenever the server restarts.
+- **Production Recommendation**: When moving to production, a persistent database (e.g., PostgreSQL) should be used. 
+- **Cleanup**: Periodic cleanup of logs older than 90 days is recommended to maintain performance.
+
+## Privacy Considerations
+- **Non-Sensitive Logging**: The system is designed to log *actions* (who, what, when) without storing sensitive payload data.
+- **Personally Identifiable Information (PII)**: 
+  - `performedBy`: Stores the user identifier (e.g., from `x-user` header).
+  - `resourceId`: Stores the identifier of the modified resource (e.g., wallet address or credit line ID).
+- **Metadata**: Only includes high-level request information (`method`, `path`). Avoid logging full request bodies or headers to prevent accidental exposure of credentials or private data.
+- **Access Control**: The `GET /api/audit/logs` endpoint should be protected by admin-level authentication in a production environment. Currently, it is publicly accessible for demonstration and development purposes.
+
+## Security
+- Audit logs are immutable via the service once created.
+- The `clearAuditLogs` method is intended for test environments and system maintenance only.

coverage.json

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+
+> [email protected] test
+> node --experimental-vm-modules node_modules/.bin/jest --coverage --reporter=json
+
+----------|---------|----------|---------|---------|-------------------
+File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
+----------|---------|----------|---------|---------|-------------------
+All files |       0 |        0 |       0 |       0 |                   
+----------|---------|----------|---------|---------|-------------------