Add Authentik identity provider deployment

- Helm chart authentik 2026.5.3 with 3 server replicas, 2 worker replicas
- CNPG PostgreSQL cluster (3 instances) with rw and ro poolers (2 instances each)
- Redis with 5Gi persistent storage
- Gateway API: identity.unkin.net and identity.k8s.syd1.au.unkin.net (HTTPS)
- LDAPS via TLSRoute on ldap.k8s.syd1.au.unkin.net and ldap.main.unkin.net
- Multi-SAN TLS via cert-manager gateway integration
- S3 storage via RadosGW (bucket: authentik)
- Vault secrets: postgres-credentials, authentik-credentials, s3-credentials
- Woodpecker ServiceAccount for terraform-authentik CI
- Platform applicationset and project updated

argocd/projects/platform.yaml

@@ -17,6 +17,8 @@ spec:
       server: https://kubernetes.default.svc
     - namespace: 'artifactapi'
       server: https://kubernetes.default.svc
+    - namespace: 'authentik'
+      server: https://kubernetes.default.svc
     - namespace: 'cert-manager'
       server: https://kubernetes.default.svc
     - namespace: 'certificates'