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/pages/admin/assets/js/views/settings.js

@@ -87,19 +87,20 @@
         var form = '<div class="soon-admin-form">' +
           Form().field('配置键', '<input class="soon-input soon-input--sm" value="' + I().esc(key) + '" disabled>') +
           Form().field('配置值', Form().input('settingVal', { value: val, type: 'textarea', rows: 5 })) +
-          '<button type="button" class="soon-btn soon-btn--sm" id="adminModalSave">保存</button></div>';
+          Form().actions('保存', 'adminModalSave') + '</div>';
         Ui().openFormModal('修改 ' + key, form, function () {
           Ui().confirm('确认保存该配置？', function () {
             var saveBtn = Ui().el('adminModalSave');
             Ui().setBtnLoading(saveBtn, true);
             Api().postJson('settings', { key: key, value: Ui().el('settingVal').value }).then(function (r) {
               if (r) {
-                layer.closeAll();
+                soonLayerDismiss();
                 soonToast('配置已保存', 'success');
                 render();
               }
             }).finally(function () {
               Ui().setBtnLoading(saveBtn, false);
+              if (typeof window.soonCleanupLayerMask === 'function') window.soonCleanupLayerMask();
             });
           });
         });