feat: Implement GDPR-compliant data export and deletion functionality

[nanaf6203-bit]

Description

For GDPR compliance, users need the ability to export their personal data and request deletion. Implement these functions in the identity contract.

Acceptance Criteria

• Add export_personal_data() message returning all user-associated data
• Data includes: identity info, reputation metrics, verification history, audit trail
• Add request_data_deletion() message (initiates deletion with timelock)
• Add confirm_data_deletion() message (after cooldown, irreversible)
• Data deletion removes PII but preserves anonymized transaction records
• Emit DataExportRequested and DataDeletionCompleted events
• Add privacy policy document hash to contract storage
• Test: export returns all user data
• Test: deletion removes identity but preserves compliance records