task: #3615781 Switch the Varbase functional testing suite to Varbase E2E (10.2.x)

Issue: https://www.drupal.org/project/varbase_layout_builder/issues/3615781

Switches the Varbase functional testing suite on 10.2.x to Varbase E2E (@vardot/varbase-e2e):

• dependency + cucumber.js require: globs + step-definition helper imports point at the package
• CI test job renamed varbase-e2e-test; env vars VARBASE_E2E_*
• HTML + PDF report generated as on the Varbase Project pipeline
• local copies of steps the package ships as built-ins removed

AI-Generated: Yes

Checkpoints:

• File an issue
• Addition/Change/Update/Fix
• Testing to ensure no regression
• Automated unit testing coverage
• Automated functional testing coverage
• UX/UI designer responsibilities
• Readability
• Accessibility
• Performance
• Security
• Developer Documentation
• User Guide Documentation
• Reviewed by human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Release notes snippet
• Release

Known unrelated red

phpstan is a pre-existing analyzer red. varbase-e2e-test: 3/6 scenarios pass; the failures are admin display pages on the branch environment — pre-existing drift, not the switch.