fix(web): 本地优先保存与 design 页体验修复

- 保存先写本地缓存，登录后可选云端同步；退出登录不再因文件操作跳转登录

- 修复 Layui 遮罩残留、design2 保存后线条、toast 被 finally 提前关闭

- 保存过程恢复 loading spinner；成功提示 2.5 秒

- 云端 payload 瘦身与体积超限提示；后端 schema 迁移与 FileService 容错

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-web/js/common/member-pay-core.js

@@ -607,6 +607,7 @@
           displayChannels: channels,
           onPaid: function () {
             layer.close(idx);
+            if (typeof window.soonCleanupLayerMask === 'function') window.soonCleanupLayerMask();
             if (typeof opts.onPaid === 'function') opts.onPaid();
           },
           onBack: opts.onBack,
@@ -617,6 +618,7 @@
       },
       end: function () {
         if (payCtrl) payCtrl.destroy();
+        if (typeof window.soonCleanupLayerMask === 'function') window.soonCleanupLayerMask();
         if (typeof opts.onClose === 'function') opts.onClose();
       },
     });