Refactor: Extract UTC parsing logic to parseUTCDate helper function

- Add parseUTCDate helper function to handle timestamp UTC parsing consistently
- Eliminates code duplication across getTimeAgo, getTimeRemaining, and expiry functions
- Applied to admin.js, app-mapbox.js, app-google.js, and app.js
- Ensures consistent UTC timezone handling throughout all frontend JavaScript
- Addresses Copilot AI feedback for better code maintainability and DRY principles

The parseUTCDate function handles the logic:
timestamp.includes('T') ? timestamp : timestamp + 'Z'

This ensures all timestamp parsing uses the same UTC interpretation logic.

public/admin.js

@@ -495,7 +495,7 @@ document.addEventListener('DOMContentLoaded', () => {
     function getTimeAgo(timestamp) {
         const now = new Date();
         // Ensure timestamp is treated as UTC if it doesn't have timezone info
-        const reportTime = new Date(timestamp.includes('T') ? timestamp : timestamp + 'Z');
+        const reportTime = parseUTCDate(timestamp);
         const diffInMinutes = Math.floor((now - reportTime) / (1000 * 60));
         
         if (diffInMinutes < 1) return 'just now';
@@ -510,6 +510,11 @@ document.addEventListener('DOMContentLoaded', () => {
         return reportTime.toLocaleDateString();
     }
     
+    // Helper function to parse UTC date
+    function parseUTCDate(timestamp) {
+        return new Date(timestamp.includes('T') ? timestamp : timestamp + 'Z');
+    }
+
     // Profanity management functions
     async function loadProfanityWords() {
         if (!profanityTableBody) return;