fix(export): 禁止账号导出下载缓存，避免重复拿到旧 tdata 包

- 前端下载地址追加 ts 时间戳参数，强制每次请求唯一 URL\n- 后端 /downloads/accounts.zip 返回 no-store/no-cache 头，禁止浏览器复用旧响应\n- 修复导出后仍下载到历史坏包（旧 tdata 无法登录）的现象

src/TelegramPanel.Web/Components/Pages/Accounts.razor

@@ -958,7 +958,8 @@
             return;
 
         var qs = string.Join(",", ids);
-        Navigation.NavigateTo($"/downloads/accounts.zip?ids={qs}&format={format}", forceLoad: true);
+        var ts = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
+        Navigation.NavigateTo($"/downloads/accounts.zip?ids={qs}&format={format}&ts={ts}", forceLoad: true);
     }
 
     private async Task<string?> SelectExportFormatAsync(int accountCount, string scopeLabel)

src/TelegramPanel.Web/Program.cs

@@ -864,6 +864,11 @@ var accountsZipDownload = app.MapGet("/downloads/accounts.zip", async (
     var zipBytes = await exporter.BuildAccountsZipAsync(accounts, cancellationToken, format);
     var formatName = format == AccountExportFormat.Tdata ? "tdata" : "telethon";
     var fileName = $"telegram-panel-accounts-{formatName}-{DateTime.UtcNow:yyyyMMdd-HHmmss}.zip";
+
+    // 下载文件禁止缓存，避免浏览器复用旧的 accounts.zip 导致“重复拿到旧导出包”。
+    http.Response.Headers.CacheControl = "no-store, no-cache, must-revalidate, max-age=0";
+    http.Response.Headers.Pragma = "no-cache";
+    http.Response.Headers.Expires = "0";
     return Results.File(zipBytes, "application/zip", fileName);
 }).DisableAntiforgery();
 if (adminAuthEnabled)