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/backend-deployment.yaml

@@ -100,6 +100,7 @@ spec:
                   key: cluster-kubeconfig-key
             - name: FRONTEND_URL
               value: {{ include "cloudhost-platform.corsOrigins" . | quote }}
+            {{- include "cloudhost-platform.buildEnv" . | nindent 12 }}
             {{- range $key, $val := .Values.backend.env }}
             - name: {{ $key }}
               value: {{ $val | quote }}