add correct date format

static/app.js

@@ -43,14 +43,18 @@ function getNextUpdateDate() {
     }
   }
 
-  const monthNames = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
-  return `${monthNames[updateMonth]} ${updateYear}`;
+  const updateDate = new Date(updateYear, updateMonth, 28);
+  const yyyy = updateDate.getFullYear();
+  const mm = String(updateDate.getMonth() + 1).padStart(2, '0');
+  const dd = String(updateDate.getDate()).padStart(2, '0');
+
+  return `${yyyy}-${mm}-${dd}`;
 }
 
 function updateNavbarUpdateDate() {
   const container = document.getElementById('update-date-display');
   if (container) {
-    container.textContent = `Next update: ${getNextUpdateDate()} 28`;
+    container.textContent = `Next update: ${getNextUpdateDate()}`;
   }
 }