fix(platform): inject ELASTIC_PASSWORD from platform secrets in production

Backend validate-production-config requires a non-default ELASTIC_PASSWORD;
read it from abrban-platform-secrets.elastic-password like other credentials.

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

backend/helm/cloudhost-platform/values.yaml

@@ -124,7 +124,7 @@ secrets:
   # Use a pre-created Secret instead of chart-managed one. Required for GitOps
   # (Argo CD renders with `helm template`, so lookup/randAlphaNum regenerate on
   # every sync). Secret must contain keys: postgres-password, jwt-secret,
-  # jwt-refresh-secret, cluster-kubeconfig-key.
+  # jwt-refresh-secret, cluster-kubeconfig-key, redis-password, elastic-password.
   existingSecret: ""
   jwtSecret: ""
   jwtRefreshSecret: ""