feat(pay): guest cash purchase with signed cookie unlock (zibll-style)

Allow pay_no_logged_in cash content orders (user_id=0), set aksrt_pay_* cookies
on paid, accept cookie in access state, and expose guest CTA on paywall/box.

assets/js/cms-download.js

@@ -413,7 +413,7 @@
 
 	function renderCashier(preview, returnFocusEl) {
 		if (!preview) return;
-		if (preview.need_login) {
+		if (preview.need_login && !preview.allow_guest) {
 			renderError('', { login_url: preview.login_url }, returnFocusEl, 'aksrt_need_login');
 			return;
 		}