feat: add ArgoCD Application and k8s manifests for frontend

- application.yaml: ArgoCD Application resource (manual sync for now,
  same pattern as nextgen-be)
- manifests/: namespace, deployment, service, ingress

manifests/02-service.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: nextgen-fe
+  namespace: nextgen-fe
+spec:
+  type: ClusterIP
+  selector:
+    app: nextgen-fe
+  ports:
+    - port: 80
+      targetPort: 80
+      protocol: TCP