Add cache-busting version parameter to app.js

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webapp/includes/footer.php

@@ -10,7 +10,7 @@
     </script>
 
     <!-- Main Application JavaScript -->
-    <script src="includes/app.js"></script>
+    <script src="includes/app.js?v=<?php echo filemtime(__DIR__ . '/app.js'); ?>"></script>
 
     <?php if (isset($additionalScripts)): ?>
         <?php echo $additionalScripts; ?>