Adding the first managed group (argocd-admins) exposed a dormant bug: the
groups resource resolved `parents` by indexing authentik_group.this itself,
which OpenTofu rejects as a self-referential block. config/groups/ had been
empty, so `tofu plan` never hit it before.
Pass `parents` through as literal group PKs instead (the resource cannot
reference itself, so parent-by-map-key was never viable). Plan is clean:
3 to add (argocd provider, application, argocd-admins group).