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/compose.css

@@ -489,8 +489,9 @@
 }
 
 .aksrt-forum-compose__draft:hover {
-    border-color: var(--color-primary);
+    border-color: color-mix(in srgb, var(--color-primary) 45%, var(--color-line, #e5e7eb));
     color: var(--color-primary);
+    background: var(--color-primary-softer, color-mix(in srgb, var(--color-primary) 6%, transparent));
 }
 
 /* ── topic cover (§7.3) ── */
@@ -646,7 +647,7 @@
 }
 
 .aksrt-forum-compose__cover-btn:hover {
-    border-color: var(--color-primary);
+    border-color: color-mix(in srgb, var(--color-primary) 45%, var(--color-line, #e5e7eb));
     color: var(--color-primary);
     background: var(--color-primary-soft);
 }