Booking Calendar <= 11.8.2 - Authenticated (Editor+) Privilege Escalation to 'data_name' Parameter

The Booking Calendar plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 11.8.2 via the `wpbc_ajax_option_save` AJAX action. The vulnerability exists because the `handle_ajax_save()` function applies per-option safeguards only to names explicitly registered via `register_option_policy()`, causing `get_option_policy()` to return an empty policy — bypassing all can_save, force_mode, and allowed_keys checks — for any unregistered option name, including core WordPress options, while an attacker-controlled `data_name` parameter passes through `sanitize_key()` and is written directly to `update_option()` without restriction. This makes it possible for authenticated attackers with Editor-level access and above to escalate their privileges to Administrator by writing core WordPress options such as `default_role=administrator` and `users_can_register=1`, then self-registering a new Administrator account. The nonce check does not meaningfully restrict this attack, as both the nonce value and nonce action are attacker-supplied POST parameters, and a valid nonce is trivially obtainable via `admin-ajax.php?action=rest-nonce`.