test: #3612488 Add functional tests for the ECA Workflow Modeler

Adds functional tests for the ECA Workflow Modeler, coexistence-safe with BPMN.iO.

Issue: https://www.drupal.org/project/varbase_project/issues/3612488

What / why

Three webship-js (Playwright + Cucumber-js) scenarios covering the Workflow Modeler (drupal/modeler, React Flow) on Varbase 11:

• The Workflow Modeler is offered on the ECA "add model" screen and opens for a new model.
• A shipped model (redirect_403_to_login) opens and renders on the Workflow Modeler's .react-flow canvas with no JavaScript errors.
• The Workflow Modeler's Review flow control is available on a model event node.

These are intentionally coexistence-safe: they assert the Workflow Modeler is offered and works, not that BPMN.iO is absent — shipped Varbase currently keeps both editors installed (BPMN.iO via the Drupal CMS recipes, Workflow Modeler via the Varbase recipe). No custom step definitions are added; the suite uses only webship-js built-ins plus the existing Varbase login/wait steps (tests/step-definitions/varbase.steps.js).

Validated 4/4 green on a real coexistence Varbase build (both editors installed side by side).

The recipe-level swap (Varbase Content Base defaulting to the Workflow Modeler) is tracked separately in Varbase Content Base MR !10 (merged) (merged): varbase_content_base!10 (merged)

.gitlab-ci.yml change is a one-line addition to the SUITE: parallel matrix (- "16-eca-workflow-modeler"), everything else byte-identical.

AI-Generated: Yes. This MR and its description were drafted with AI assistance per the Drupal AI policy.

Checkpoints

• File an issue about this project
• Addition/Change/Update/Fix to this project
• Testing to ensure no regression
• Automated unit/functional testing coverage
• Developer Documentation support on feature change/addition
• User Guide Documentation support on feature change/addition
• UX/UI designer responsibilities
• Accessibility and Readability
• Reviewed by a human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Update Release Notes
• Release