fix: use harbor-core internal K8s service for docker push

Replace harbor.fireflylab.local (external DNS, not resolvable from pods)
with harbor-core.harbor.svc.cluster.local (internal ClusterIP, always resolvable).
DinD insecure-registry flag allows HTTP to the internal service.
values.yaml image.repository stays as harbor.fireflylab.local so kubelet
pulls via the external hostname (same image, different access path).

Jenkinsfile

@@ -19,6 +19,8 @@ spec:
     env:
     - name: DOCKER_TLS_CERTDIR
       value: ""
+    args:
+    - --insecure-registry=harbor-core.harbor.svc.cluster.local
   - name: tools
     image: alpine/git
     command:
@@ -31,7 +33,7 @@ spec:
 
     environment {
         APP_NAME        = 'tictactoe'
-        HARBOR_REGISTRY = 'harbor.fireflylab.local'
+        HARBOR_REGISTRY = 'harbor-core.harbor.svc.cluster.local'
         HARBOR_PROJECT  = 'library'
         IMAGE           = "${HARBOR_REGISTRY}/${HARBOR_PROJECT}/${APP_NAME}"
         DOCKER_HOST     = 'tcp://localhost:2375'