Add comprehensive audit logging for all sensitive operations

[Smartdevs17]

Description

Sensitive operations (payment initiation, account changes, admin actions) are not logged for audit purposes. Implement structured audit logging with tamper-evident storage.

Acceptance Criteria

• Audit event schema with actor, action, resource, timestamp
• Tamper-evident log storage (append-only with hash chain)
• Audit query API with filtering and export
• Real-time audit alerting for critical events
• Audit log retention with archival policy
• Compliance reporting (SOC2, PCI-DSS relevant fields)

Technical Scope

• backend/src/services/auditService.ts
• backend/src/routes/audit.ts
• Edge: log injection attacks, storage costs for high-volume events, clock synchronization

[itsjoetruthofficial-lang]

@itsjoetruthofficial-lang has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to work on this issue.

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[drips-wave]

Congratulations, @itsjoetruthofficial-lang! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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