Add encrypted audit log export

[jasdumas]

Problem

Security logs stored in plaintext at ~/.counselor/security_logs/ may contain sensitive information (code snippets, file paths). Organizations with compliance requirements need secure log handling.

Proposed Solution

• Add export_audit_logs() function with optional encryption
• Support GPG/age encryption for log exports
• Add log rotation and retention policies
• Support structured log formats (JSON lines) for SIEM integration
• Option to redact code content while preserving event metadata

Acceptance Criteria

• Logs can be exported in encrypted format
• Configurable retention period with automatic cleanup
• JSON lines format for external tool integration
• Sensitive content redaction option