feat(helm): add cloudhost-app Helm chart for all runtimes

- deployment.yaml with imagePullSecrets, health probes, WordPress volumes
- db-deployment.yaml for PostgreSQL/MySQL with readiness/liveness probes
- ingress.yaml with cert-manager TLS
- registry-pull-secret.yaml for insecure registries
- PVCs and secrets with helm.sh/resource-policy: keep
- _helpers.tpl with shared template functions
- values.yaml with comprehensive defaults

backend/helm/cloudhost-app/templates/registry-pull-secret.yaml

@@ -0,0 +1,13 @@
+{{- $name := include "cloudhost-app.name" . -}}
+{{- $ns   := include "cloudhost-app.namespace" . -}}
+{{- $registryUrl := .Values.registry.url | default "localhost:30500" -}}
+apiVersion: v1
+kind: Secret
+metadata:
+  name: registry-pull-secret
+  namespace: {{ $ns }}
+  labels:
+    {{- include "cloudhost-app.labels" . | nindent 4 }}
+type: kubernetes.io/dockerconfigjson
+data:
+  .dockerconfigjson: {{ printf `{"auths":{"%s":{"auth":""}}}` $registryUrl | b64enc | quote }}