CHORE(test): update about-us page text

- Modify text for ArgoCD image updater test
- Verify automated deployment pipeline

nextjs/app/about-us/page.tsx

@@ -1,3 +1,3 @@
 export default function AboutUs(){
-    return <div>Practice app for K8s/argoCD/Grafana</div>
+    return <div>Practice app for K8s/argoCD/Grafana - Updated at 2026-01-09 16:02 KST</div>
 }