Fix self-referential authentik_group parents

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).

config/groups/argocd-admins.yaml

@@ -0,0 +1,3 @@
+# Members of this group get ArgoCD role:admin (mapped in argocd-rbac-cm).
+# Everyone else who logs in via Authentik gets role:readonly.
+name: argocd-admins

config/providers_oauth2/argocd.yaml

@@ -0,0 +1,21 @@
+# OAuth2/OIDC provider + application for the in-cluster ArgoCD
+# (argocd.k8s.syd1.au.unkin.net). client_secret is read from Vault, not committed.
+name: ArgoCD
+authorization_flow: default-provider-authorization-implicit-consent
+invalidation_flow: default-provider-invalidation-flow
+client_type: confidential
+client_id: argocd
+client_secret_vault:
+  mount: kv
+  path: kubernetes/namespace/argocd/default/oauth-credentials
+scope_mappings:
+  - goauthentik.io/providers/oauth2/scope-openid
+  - goauthentik.io/providers/oauth2/scope-email
+  - goauthentik.io/providers/oauth2/scope-profile
+redirect_uris:
+  # Web UI SSO callback.
+  - matching_mode: strict
+    url: https://argocd.k8s.syd1.au.unkin.net/auth/callback
+  # `argocd login --sso` CLI callback (local listener).
+  - matching_mode: strict
+    url: http://localhost:8085/auth/callback

modules/authentik/main.tf

@@ -3,7 +3,7 @@ resource "authentik_group" "this" {
 
   name         = each.value.name
   is_superuser = each.value.is_superuser
-  parents      = each.value.parents != null ? [for p in each.value.parents : authentik_group.this[p].id] : []
+  parents      = each.value.parents
   attributes   = jsonencode(each.value.attributes)
 }
 

modules/authentik/variables.tf

@@ -2,8 +2,10 @@ variable "groups" {
   type = map(object({
     name         = string
     is_superuser = optional(bool, false)
-    parents      = optional(list(string), null)
-    attributes   = optional(map(string), {})
+    # PKs of existing parent groups. These must be literal group PKs, not keys
+    # into this map: authentik_group cannot reference itself.
+    parents    = optional(list(string), null)
+    attributes = optional(map(string), {})
   }))
   default = {}
 }