chore(iam): retire Authentik

Zitadel is running and has provisioned OIDC clients for all 12 consumers
(state.json: kubernetes, paperless, forgejo, argocd, grafana, immich, minio,
vault, poimen, api-gw, queue-sqs, homarr). Authentik's remaining job was to
serve until the last consumer moved.

Remove every Authentik artifact from GitOps:
- ArgoCD Application `authentik` and its Helm values
- ArgoCD Application `iam-jobs` (provisioner RBAC + migration job)
- ArgoCD Application `oidc-bootstrap` (one-shot apiserver restart)
- authentik-db CNPG cluster definition
- authentik-secrets SOPS file and secret-generator entry
- Ingress rule, cloudflared tunnel hostname, CoreDNS rewrite
- Prometheus alerts and ServiceMonitor
- admin OIDC ClusterRoleBinding provisioning binding
- scripts/iam/provision-rbac.py (the Authentik provisioner)

The chart repo https://charts.goauthentik.io is removed from the AppProject.

Kube-apiserver OIDC and consumer configs are switched to Zitadel in the
local cluster-config (gitignored) and applied separately via talosctl.

k8s/bootstrap/ingress/ingress.yaml

@@ -275,31 +275,3 @@ spec:
                 name: temporal-web
                 port:
                   number: 8080
-
----
-# ── Authentik (identity provider) ─────────────────────────────────────────────
-# The chart's ingress is disabled in k8s/infra/iam/authentik-values.yaml; the
-# rule lives here so ingress-config owns every hostname. TLS terminates at
-# nginx via the wildcard default-ssl-certificate, so the backend stays HTTP.
-apiVersion: networking.k8s.io/v1
-kind: Ingress
-metadata:
-  name: authentik
-  namespace: iam
-  annotations:
-    nginx.ingress.kubernetes.io/proxy-body-size: "16m"
-    nginx.ingress.kubernetes.io/proxy-read-timeout: "3600"
-    nginx.ingress.kubernetes.io/proxy-send-timeout: "3600"
-spec:
-  ingressClassName: nginx
-  rules:
-    - host: authentik.riotpiao.com
-      http:
-        paths:
-          - path: /
-            pathType: Prefix
-            backend:
-              service:
-                name: authentik-server
-                port:
-                  number: 80