feat: integrate Quagga2 scanner, background pagination, and secure fetch API

Configure Quagga2 barcode scanner with environment facing mode
Add fallback keyboardScanKeydownHandler for physical keyboard-wedge scanners
Secure fetch requests by including X-CSRFToken headers
Implement loadRemainingLibraryItemsInBackground for seamless data loading
Refactor showItemDetail to accurately render videos, external URLs, and local uploa

Web/app.py

@@ -2659,6 +2659,12 @@ def upload_student_cards_excel():
     """Bulk import student cards from Excel."""
     return _upload_student_cards_excel()
 
+@app.route('/api/is_student_card/<id>', methods=['POST'])
+def is_student_card(id):
+    user = sanitize_form_value(id)
+    exists = bool(us.student_card_exists(user))
+    return jsonify({"is_student_card": exists})
+
 """-------------------------------------------------------------File Serving-----------------------------------------------------------------------------"""