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/infra/rbac/grafana-operator-role.yaml

@@ -0,0 +1,35 @@
+# Scoped operator access for grafana-admins: dashboards + admin creds only.
+# grafana-oidc (client secret) stays excluded - editing it is a security
+# change, not app config. Inert until kube-apiserver's OIDC wiring lands.
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: grafana-operator
+  namespace: logging
+rules:
+  - apiGroups: ["apps"]
+    resources: ["deployments"]
+    resourceNames: ["grafana"]
+    verbs: ["get", "list", "watch", "update", "patch"]
+  - apiGroups: [""]
+    resources: ["configmaps"]
+    resourceNames: ["grafana-dashboards-default", "grafana-config-dashboards"]
+    verbs: ["get", "list", "watch", "update", "patch"]
+  - apiGroups: [""]
+    resources: ["secrets"]
+    resourceNames: ["grafana-admin"]
+    verbs: ["get", "list", "watch", "update", "patch"]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: grafana-admins-binding
+  namespace: logging
+subjects:
+  - kind: Group
+    name: "oidc:grafana-admins"
+    apiGroup: rbac.authorization.k8s.io
+roleRef:
+  kind: Role
+  name: grafana-operator
+  apiGroup: rbac.authorization.k8s.io