Adopt the Workflow Modeler as the default ECA editor and add functional testing

Problem/Motivation

Varbase ships the BPMN.iO modeler for ECA via the Varbase Content Base recipe. The React-Flow-based Workflow Modeler (drupal/modeler) is a modern editor for the same Modeler API models, adds live execution replay (Review flow), and opens all existing BPMN.iO-authored models with no migration (a model is the eca.eca.* config entity; the editor only re-derives the diagram). Varbase 11 should adopt it as the default ECA editor, and this workflow area should be covered by functional tests.

Steps to reproduce

N/A. This is a tracking issue, not a bug report.

Proposed resolution

1. Recipe change (done, under review): Varbase Content Base enables modeler instead of bpmn_io, requires drupal/modeler, retags its two shipped ECA models to modeler_id: workflow_modeler, and stops shipping BPMN.iO raw diagram data. bpmn_io remains available as a transitive dependency but is not enabled by the recipe. Tracked in: Varbase Content Base issue https://www.drupal.org/project/varbase_content_base/issues/3612486 and MR https://git.drupalcode.org/project/varbase_content_base/-/merge_requests/10
2. Add functional tests (webship-js / Playwright + Cucumber-js) covering: the Workflow Modeler is offered on the ECA add screen; existing models open and render in it; a model still executes; BPMN.iO edit routes are gone after the swap.

AI-Generated: Yes. This issue summary was drafted with AI assistance per the Drupal AI policy.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project (recipe swap done, in review, see linked issue and MR above)
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage (functional tests in progress)
• ➖ Developer Documentation support on feature change/addition (Varbase docs 11.0.x developers/varbase-eca update pending)
• ➖ 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

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• Varbase now uses the Workflow Modeler (React Flow) as the default visual editor for ECA workflows. Existing BPMN.iO-authored models continue to work and open in the new editor with no migration.