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/argocd/apps/40-data.yaml

@@ -1,4 +1,4 @@
-# Wave 2 — dedicated per-app CNPG Postgres clusters (authentik-db → ns iam,
+# Wave 2 — dedicated per-app CNPG Postgres clusters (zitadel-db → ns iam,
 # temporal-db + visibility → ns temporal). ONE App, ONE folder (k8s/infra/databases).
 # CNPG operator is Phase-0 bootstrap; these Cluster CRs are GitOps — no circular
 # dep (they run after ArgoCD is up, before their apps at w3/w8). CNPG generates