docs: Update certificate testing documentation and methodology

This commit:
- Creates comprehensive CERTIFICATE_TESTING_GUIDE.md to document certificate testing
- Updates TRAINER_JOURNEY_TEST_SUMMARY.md to include certificate functionality
- Updates main README.md with certificate testing information
- Creates a centralized Config.ts utility for consistent configuration
- Updates CertificatePage.ts and other page objects for consistency
- Creates a guided manual test script (run-certificate-tests.sh)
- Archives outdated certificate test files
- Improves documentation organization and consistency

The changes address issues with the Playwright test configuration by providing a guided
manual testing approach while maintaining the best practices of code organization,
error handling, and proper documentation.

This ensures that the certificate functionality can be reliably tested while providing
a path to future automated testing once configuration issues are resolved.