feat: add homelab-wide Authentik RBAC model and k8s OIDC auth wiring

Adds permissions claim + per-service admin groups in Authentik, scoped
Role/RoleBinding per service, public PKCE kubernetes OAuth2 client, and
kube-apiserver OIDC extraArgs. Also fixes paperless OIDC signup permissions
via adapter override and adds CoreDNS rewrite for authentik.riotpiao.com.

k8s/apps/paperless/kustomization.yaml

@@ -9,6 +9,8 @@ resources:
   - service.yaml
   - ingress.yaml
   - backup-cronjob.yaml
+  - adapter-configmap.yaml
+  - rbac.yaml
 # postgres: paperless-db CNPG Cluster, deployed by k8s/infra/databases (wave 2,
 # before this app at wave 8) - not duplicated here. Same for the paperless-oidc
 # and paperless-minio-creds Secrets, written by PostSync provisioning Jobs in