Port the v1 webhook webtest to /api/v2 and extend it to the full
permission gradient the model enforces: list needs read access while
create/update/delete need write (Project.CanWrite), exercised across an
owned project and read/write/admin shares plus a no-access project. Also
assert credential masking, events-only updates, the 412 validation path,
and that the routes 404 when webhooks.enabled is false.
Add fixture webhooks 2-5 in projects 9/10/11/2 to back the matrix; they
do not collide with the e2e tests, which scope to project 1.
kolaente