CHW-4214 BuiltinRoleImmutable

built-in roles cannot be edited or deleted; create a custom role instead

Default message: built-in roles cannot be edited or deleted; create a custom role instead
HTTP status: 400 (client)

Problem. The caller tried to edit or delete a built-in role. Cause. Built-in roles are managed in code; their permissions are part of the RBAC contract. Fix. Create a custom role with the desired permission set instead. HTTP 400.