feat: implement data anonymization pipeline for analytics exports (#614)

[euniceamoni]

• Add GDPR PII field registry with sensitivity classifications
• Add anonymization strategies: mask (email), hash (SHA-256+salt), truncate (IP), perturb (date ±3 days)
• Add AnonymizationPipeline orchestrator with full/pseudonymized/anonymized export levels
• Add AnonymizationController with role-based access (admin/analytics/third-party)
• Add export audit log written to shared PII audit trail
• Add k-anonymity check (warn if group < 5 records)
• Add re-identification risk warning for datasets < 20 records
• Add preview endpoint (up to 5 sample rows)
• Irreversible guarantee: export salt discarded for anonymized exports
• 44 passing tests

Pull Request Checklist

Quality Gates (All must pass before merge)

• Lint: Code passes ESLint and Prettier checks
• Type Check: TypeScript compilation succeeds
• Tests: All tests pass closes Implement data anonymization pipeline for analytics exports #614
• Build: Project builds successfully
• Rust Format: Smart contract formatting is correct
• Rust Clippy: Smart contract linting passes
• Rust Tests: All smart contract tests pass
• Rust Build: Smart contracts compile successfully

Additional Requirements

• New code has appropriate TypeScript types
• No hardcoded secrets or credentials
• New features have corresponding tests
• Documentation updated if needed

Reviewers

• At least 1 approval required for merge
• All CI checks must be green

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This PR will not be mergeable until all quality gates pass.

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