RAILIANCE-WP-0003 T02-T06: provision shared apps-pg cnpg cluster

Adds the shared CloudNativePG cluster apps-pg for S5 application
databases:
- helm/apps-pg-cluster.yaml — Cluster CR, PG 16, 1 instance, 10Gi
- helm/apps-pg-networkpolicies.yaml — egress-to-kube-api +
  ingress-from-cnpg-operator + label-based ingress opt-in
  (railiance.io/postgres-client=apps-pg)
- helm/apps-pg-secret.sops.yaml.template — bootstrap credential
  template (encrypt with SOPS before committing the real .sops.yaml)
- Makefile targets: apps-pg-deploy, apps-pg-status (with cnpg-plugin
  fallback), apps-pg-shell (apps_admin/apps_meta), apps-pg-logs
- docs/apps-pg.md (codex) — consumer onboarding contract clarifying
  the CNPG 1.28 role/database lifecycle boundary

Also fixes helm/gitea-db-cluster.yaml: spec.postgresql.version is not
a valid CNPG v1 field (strict decoding rejects it). Replaced with
spec.imageName matching the live cluster (postgresql:18.1-system-trixie)
so make db-deploy is a no-op instead of an apply rejection.

Live state at commit time: Cluster apps-pg in healthy state, primary
apps-pg-1 Running, smoke-tested via psql from a labeled temp ns.

Co-Authored-By: codex <noreply@openai.com>
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

helm/gitea-db-cluster.yaml

@@ -24,8 +24,10 @@ metadata:
     railiance.io/layer: s3-platform
 spec:
   instances: 1   # bump to 3 when node RAM > 8GB
-  postgresql:
-    version: "16"
+  # spec.postgresql.version is not a real CNPG v1 field; use imageName.
+  # Live cluster was upgraded to PG 18.1; match the live state so
+  # `make db-deploy` (kubectl apply) is a no-op rather than a rejection.
+  imageName: ghcr.io/cloudnative-pg/postgresql:18.1-system-trixie
   storage:
     size: 10Gi
   bootstrap: