feat(forum): multi-gateway cashier for pay-visibility topics

Replace balance-only AJAX topic purchase with AKSRT_Topic_Pay REST
cashier (resource orders + Payment_Gateway), reuse cms-download modal,
and unlock on aksrt_order_paid.

assets/js/forum-governance.js

@@ -675,49 +675,6 @@
         });
     }
 
-    function bindPurchaseButton(button) {
-        button.addEventListener('click', function () {
-            var topicId = parseInt(button.getAttribute('data-topic-id') || '0', 10);
-            var price = button.getAttribute('data-price') || '0';
-            var isFree = button.getAttribute('data-free') === '1';
-            var feedback = button.parentElement ? button.parentElement.querySelector('.js-aksrt-action-feedback') : null;
-
-            if (!topicId) {
-                return;
-            }
-
-            var confirmMsg = isFree
-                ? '确认使用 VIP 免费解锁此主题？'
-                : ('确认使用余额支付 ¥' + price + ' 购买此主题？');
-            if (!window.confirm(confirmMsg)) {
-                return;
-            }
-
-            button.disabled = true;
-            setFeedback(feedback, isFree ? '正在解锁…' : '正在支付…', 'is-loading');
-
-            var data = new FormData();
-            data.append('action', 'aksrt_forum_purchase_topic');
-            data.append('topic_id', topicId);
-            data.append('_nonce', rootData.forumNonce || '');
-
-            fetch((rootData.ajaxUrl || '/wp-admin/admin-ajax.php'), {
-                method: 'POST',
-                body: data,
-                credentials: 'same-origin',
-            }).then(function (r) { return r.json(); }).then(function (payload) {
-                if (!payload.success) {
-                    throw new Error((payload.data && payload.data.message) || '购买失败');
-                }
-                setFeedback(feedback, '购买成功，正在刷新…', 'is-success');
-                setTimeout(function () { window.location.reload(); }, 800);
-            }).catch(function (error) {
-                setFeedback(feedback, error.message || '购买失败', 'is-error');
-                button.disabled = false;
-            });
-        });
-    }
-
     function formatFollowPayLabel(pay) {
         pay = pay || {};
         if (pay.is_free) {
@@ -1558,7 +1515,6 @@
         document.querySelectorAll('.js-aksrt-topic-score').forEach(bindScoreButton);
         document.querySelectorAll('.js-aksrt-adopt-answer').forEach(bindAdoptButton);
         document.querySelectorAll('.js-aksrt-unlock-topic').forEach(bindUnlockButton);
-        document.querySelectorAll('.js-aksrt-purchase-topic').forEach(bindPurchaseButton);
         document.querySelectorAll('.js-aksrt-follow-plate').forEach(bindFollowPlateButton);
         bindForumCommentEngine();
         bindForumHomeTabs();