feat(smart-contract): Add Comprehensive Security Audit Trail and Anomaly Detection

[devJaja]

Summary

Implement an on-chain security audit trail that logs all administrative and high-value operations with anomaly detection for suspicious patterns.

Motivation

Security incidents require forensic analysis. An immutable audit trail enables post-incident investigation and real-time anomaly alerts.

Acceptance Criteria

• All admin operations logged with caller, timestamp, and operation details
• High-value operations (>100 XLM) flagged for additional logging
• get_audit_log returns paginated audit history
• Anomaly detection: flag operations outside normal patterns
• Rate limiting: alert if >N operations from same caller in time window
• Events: AuditLogEntry, AnomalyDetected
• Log entries stored with TTL (default 1 year)
• Unit tests for logging, querying, and anomaly detection

Files to Modify

File	Action
smart-contracts/contracts/agent_registry/src/lib.rs	Add audit logging functions
smart-contracts/contracts/agent_registry/src/types.rs	Add AuditLogEntry struct
smart-contracts/contracts/agent_registry/src/events.rs	Add audit and anomaly events
smart-contracts/contracts/agent_registry/src/test.rs	Add audit trail tests
smart-contracts/docs/security.md	New: security audit documentation

How to Contribute

1. Create branch feat/on-chain-audit-trail
2. Design audit log storage structure
3. Implement logging for all admin operations
4. Add anomaly detection logic
5. Write comprehensive unit tests
6. Run cargo test and cargo clippy before submitting PR