feat: add GitOps structure for kubernetes-dashboard, n8n, xslt-lab

- apps/kubernetes-dashboard: raw manifests (namespace, rbac, deployment, service, ingress)
- apps/n8n: Helm values referencing existing n8n-postgresql secret (no password in git)
- apps/xslt-lab: Helm values for xslt-playground chart
- argocd/applications: ArgoCD Application CRDs for all three apps

apps/kubernetes-dashboard/service.yaml

@@ -0,0 +1,11 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: kubernetes-dashboard
+  namespace: kubernetes-dashboard
+spec:
+  ports:
+  - port: 443
+    targetPort: 8443
+  selector:
+    k8s-app: kubernetes-dashboard