fix: Use Number.isNaN in formatUpdateTime

Replaces isNaN with Number.isNaN for checking invalid date in formatUpdateTime method to improve type safety and accuracy.

Author: ReenigneArcher

gh-pages-template/assets/js/app.js

@@ -225,7 +225,7 @@ class UIManager {
     formatUpdateTime(isoString) {
         if (!isoString) return '-';
         const date = new Date(isoString);
-        if (isNaN(date.getTime())) return isoString;
+        if (Number.isNaN(date.getTime())) return isoString;
         return date.toLocaleString();
     }