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/rbac.yaml

@@ -0,0 +1,35 @@
+# Scoped operator access for paperless-admins: restart/config-edit rights on
+# just this service's own resources, nothing CNPG-managed (paperless-db-*)
+# or provisioning-managed (paperless-oidc, paperless-minio-creds). Inert
+# until kube-apiserver's OIDC wiring lands (--oidc-groups-claim=groups,
+# --oidc-groups-prefix=oidc:) - subject name below assumes that prefix.
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: paperless-operator
+rules:
+  - apiGroups: ["apps"]
+    resources: ["deployments"]
+    resourceNames: ["paperless"]
+    verbs: ["get", "list", "watch", "update", "patch"]
+  - apiGroups: [""]
+    resources: ["configmaps"]
+    resourceNames: ["paperless-config"]
+    verbs: ["get", "list", "watch", "update", "patch"]
+  - apiGroups: [""]
+    resources: ["secrets"]
+    resourceNames: ["paperless-secrets"]
+    verbs: ["get", "list", "watch", "update", "patch"]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: paperless-admins-binding
+subjects:
+  - kind: Group
+    name: "oidc:paperless-admins"
+    apiGroup: rbac.authorization.k8s.io
+roleRef:
+  kind: Role
+  name: paperless-operator
+  apiGroup: rbac.authorization.k8s.io