Gravity Flow decision: gate gravityflow_cancel_workflow behind GRAVITY_FORMS_ALLOW_DELETE?

[marceldarvas]

gravityflow_cancel_workflow is currently ungated. Rationale at implementation: it's a POST (not an HTTP DELETE) and is reversible via gravityflow_restart_workflow, and the existing GRAVITY_FORMS_ALLOW_DELETE guard only gates true deletes.

Decision needed

• Keep ungated (current behavior), or
• Gate cancel_workflow behind GRAVITY_FORMS_ALLOW_DELETE for parity with the delete-safety posture.

Open question #2 from docs/gravity-flow-review-brief.md. Cheap to change either way — one guard check in src/gravity-flow-client.js.

Branch: feat/gravity-flow