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/auth-session.js

@@ -85,16 +85,21 @@
       fullUrl = getApiBase() + '/' + String(url).replace(/^\/+/, '');
     }
 
+    var hadSession = !!(token || getRefreshToken());
+
     return fetch(fullUrl, opts).then(function (response) {
       if (response.status !== 401) return response;
+      if (!getRefreshToken()) return response;
       return refreshAccessToken().then(function (newToken) {
         var retryHeaders = Object.assign({}, opts.headers || {});
         retryHeaders['Authorization'] = 'Bearer ' + newToken;
         var retryOpts = Object.assign({}, opts, { headers: retryHeaders });
         return fetch(fullUrl, retryOpts);
       }).catch(function () {
-        clearSession();
-        redirectToLogin();
+        if (hadSession) {
+          clearSession();
+          redirectToLogin();
+        }
         return response;
       });
     });