Fix timezone handling for accurate 48-hour expiry display

- Fixed getTimeAgo(), getTimeRemaining(), and getRemainingClass() functions
- Database stores UTC timestamps but frontend was treating them as local time
- Added logic to append 'Z' to timestamps without timezone info to force UTC interpretation
- Now properly shows 48-hour countdown instead of incorrect 52-hour or 28-hour values
- Affects both main app (app-mapbox.js) and admin panel (admin.js)

public/admin.js

@@ -494,7 +494,8 @@ document.addEventListener('DOMContentLoaded', () => {
 
     function getTimeAgo(timestamp) {
         const now = new Date();
-        const reportTime = new Date(timestamp);
+        // Ensure timestamp is treated as UTC if it doesn't have timezone info
+        const reportTime = new Date(timestamp.includes('T') ? timestamp : timestamp + 'Z');
         const diffInMinutes = Math.floor((now - reportTime) / (1000 * 60));
         
         if (diffInMinutes < 1) return 'just now';