Change last refresh time display format to system locale

frontend-modern/src/App.tsx

@@ -368,11 +368,10 @@ function App() {
   const formatLastUpdate = (timestamp: string) => {
     if (!timestamp) return '';
     const date = new Date(timestamp);
-    return date.toLocaleTimeString('en-US', {
+    return date.toLocaleTimeString(undefined, {
       hour: 'numeric',
       minute: '2-digit',
-      second: '2-digit',
-      hour12: true
+      second: '2-digit'
     });
   };