fix(security): add role checks to 7 admin endpoints, fix undefined vars in admin_update_passenger, add input validation to send_whatsapp

backend/Admin/AdminCaptain/get.php

@@ -1,6 +1,12 @@
 <?php
 require_once __DIR__ . '/../../connect.php';
 
+if ($role !== 'admin' && $role !== 'super_admin') {
+    http_response_code(403);
+    echo json_encode(['error' => 'Unauthorized: Admin access required']);
+    exit;
+}
+
 $sql = "SELECT
     `driver`.`id`,
     `driver`.`phone`,