fix: remove hardcoded GW_URL from staging manifest

GW_URL in the K8s manifest was injected into all appsettings*.json files
by docker-entrypoint.sh, overriding even appsettings.Production.json.
Now only BLAZOR_ENVIRONMENT is set; GwUrl comes from the correct
appsettings.{Environment}.json per environment.

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

k8s/staging/backoffice-deployment.yaml

@@ -27,8 +27,6 @@ spec:
         env:
         - name: BLAZOR_ENVIRONMENT
           value: "Staging"
-        - name: GW_URL
-          value: "https://cms.se.kbs1.ir"
         resources:
           requests:
             memory: "128Mi"