fix(build): default Kaniko and init images to Harbor via Helm values

User-app builds no longer pull gcr.io/docker.io directly when build.images
is configured in values.yaml, fixing ImagePullBackOff on clusters without
upstream registry access.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/helm/cloudhost-platform/templates/_helpers.tpl

@@ -113,3 +113,14 @@ PLATFORM_DOMAIN / preview domain from the first entry only. The panel host
 {{- define "cloudhost-platform.frontendImage" -}}
 {{- printf "%s:%s" .Values.images.frontend.repository .Values.images.frontend.tag }}
 {{- end }}
+
+{{- define "cloudhost-platform.buildEnv" -}}
+- name: KANIKO_IMAGE
+  value: {{ .Values.build.images.kaniko | quote }}
+- name: BUILD_ALPINE_IMAGE
+  value: {{ .Values.build.images.alpine | quote }}
+- name: BUILD_ALPINE_GIT_IMAGE
+  value: {{ .Values.build.images.alpineGit | quote }}
+- name: BASE_IMAGE_REGISTRY
+  value: {{ .Values.build.baseImageRegistry | quote }}
+{{- end }}