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/app-mapbox.js

@@ -93,10 +93,15 @@ document.addEventListener('DOMContentLoaded', async () => {
         });
     };
     
+    // Helper function to parse UTC date
+    const parseUTCDate = (timestamp) => {
+        return new Date(timestamp.includes('T') ? timestamp : timestamp + 'Z');
+    };
+
     const 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';
@@ -174,7 +179,7 @@ document.addEventListener('DOMContentLoaded', async () => {
         
         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 expirationTime = new Date(reportTime.getTime() + 48 * 60 * 60 * 1000);
         const remaining = expirationTime - now;
         
@@ -198,7 +203,7 @@ document.addEventListener('DOMContentLoaded', async () => {
         
         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 expirationTime = new Date(reportTime.getTime() + 48 * 60 * 60 * 1000);
         const remaining = expirationTime - now;
         const hoursRemaining = remaining / (1000 * 60 * 60);