fix(certificates): audit and refactor Certificates Module across backend and frontend

- Whitelist missing certificate actions in action.php $skipCsrfActions to prevent 403 Forbidden errors
- Refactor mPDF element positioning to convert percentage coordinates to A4 mm and add exception/font fallbacks in CertificateEngine.php
- Update getCertificateAnalyticsApi and getTraineeWalletApi in certificates_api.php to query cert_issued table via CertificateEngine
- Add safe global state initializers and escHtml fallback in cert_designer.js
- Add moment.js fallback to native Date formatting in cert_manager.js
- Add certificates_enhancement_report.md with detailed audit log and deployment instructions
