feat: deploy Immich with Authentik OIDC, rock as admin

Self-hosted photo backup (Google Photos replacement) - raw manifests,
no Helm chart, self-contained under k8s/apps/immich including its own
CNPG Postgres. Media PVC shares the cp-3 HDD 2TB/2TB with
paperless-media.

Postgres is pg18, not this repo's usual 16.2: CNPG's official pgvector
extension image (ghcr.io/cloudnative-pg/pgvector) is only published
for pg18, loaded via CNPG's ImageVolume extension mechanism (operator
1.30.0 / k8s 1.36.1 both support it). Immich auto-manages CREATE
EXTENSION itself at startup.

OIDC via a new "immich_role" Authentik scope mapping (homelab-admins/
immich-admins -> "admin" claim, else "user"), consumed by Immich's
OAuth roleClaim setting which re-syncs isAdmin on every login - more
reliable than Immich's racy first-user-is-admin fallback. Config
composed into an immich-oidc Secret and mounted as IMMICH_CONFIG_FILE,
matching the paperless-oidc pattern. k8s RBAC (immich-operator Role +
oidc:immich-admins binding) mirrors paperless/rbac.yaml.

immich namespace pre-created in k8s/infra/databases/namespaces.yaml
(not just immich's own CreateNamespace=true) since the iam PostSync
job's RoleBinding needs it to exist before wave 8.

k8s/infra/databases/namespaces.yaml

@@ -16,3 +16,11 @@ apiVersion: v1
 kind: Namespace
 metadata:
   name: paperless
+---
+# Needed here (not just immich's own CreateNamespace=true at wave 8) because
+# k8s/infra/iam's PostSync job (wave 3) has a RoleBinding targeting this
+# namespace - same ordering reason as paperless above.
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: immich