fix(polish): 订单购物车论坛粉边软化 + 论坛付费帖购链路

- 购物车/商品/论坛表面复用 #77 soft recipe（mix 边 + soft ring）
- 论坛 visibility=pay：订单 resource + 余额扣费闭环
- VIP 价/免费解锁 + 购买 CTA/AJAX，复用现有 Order/Credits

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/css/frontend/forum/extras/reply-action-buttons.css

@@ -16,7 +16,7 @@
 
 .aksrt-forum-reply__reply-btn:hover,
 .aksrt-forum-reply__top-btn:hover {
-    color: var(--c-primary, #1890ff);
+    color: var(--color-primary);
 }
 
 /* ── §7.3 Hidden content block [aksrt_hide] ── */
@@ -80,13 +80,13 @@
 
 .aksrt-forum-home-tabs__btn:hover {
     color: var(--c-text-1, #333);
-    border-color: var(--c-primary, #1890ff);
+    border-color: color-mix(in srgb, var(--color-primary) 45%, var(--color-line, #e5e7eb));
 }
 
 .aksrt-forum-home-tabs__btn.is-active {
-    background: var(--c-primary, #1890ff);
+    background: var(--color-primary);
     color: #fff;
-    border-color: var(--c-primary, #1890ff);
+    border-color: color-mix(in srgb, var(--color-primary) 45%, var(--color-line, #e5e7eb));
 }
 
 .aksrt-forum-home-tabs__badge {