feat: add MetalLB for on-premise LoadBalancer support

- Add MetalLB IPAddressPool (192.168.108.213/32) and L2Advertisement
  so the frontend gets a stable external IP on the LAN
- Change frontend service type: NodePort → LoadBalancer
- Add 'Setup MetalLB' stage in Jenkinsfile that installs MetalLB v0.14.8
  (idempotent) and applies the IP pool config before each deploy

After deploy: kubectl get svc frontend -n scrum-manager
should show EXTERNAL-IP: 192.168.108.213
App accessible at: http://192.168.108.213

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Jenkinsfile

@@ -110,6 +110,24 @@ pipeline {
             }
         }
 
+        stage('Setup MetalLB') {
+            steps {
+                withKubeConfig([credentialsId: "${K8S_CRED_ID}"]) {
+                    sh """
+                        # Install MetalLB if not already present (idempotent)
+                        kubectl apply -f https://raw.githubusercontent.com/metallb/metallb/v0.14.8/config/manifests/metallb-native.yaml
+
+                        # Wait for MetalLB controller and speaker to be ready
+                        kubectl rollout status deployment/controller -n metallb-system --timeout=90s
+                        kubectl rollout status daemonset/speaker    -n metallb-system --timeout=90s
+
+                        # Apply IP pool config — CRDs must be ready before this
+                        kubectl apply -f k8s/overlays/on-premise/metallb/
+                    """
+                }
+            }
+        }
+
         stage('Deploy to K8s') {
             steps {
                 withKubeConfig([credentialsId: "${K8S_CRED_ID}"]) {