增强打印预览功能，新增离线打印功能，新增缩放控制按钮以提升用户体验。优化打印数据准备逻辑，支持实时预览缩放，确保打印效果的一致性。同时，重构相关视图和服务以增强系统的可维护性和扩展性。

yy-admin-master/YY.Admin/ViewModels/LoginWindowViewModel.cs

@@ -5,6 +5,7 @@ using Microsoft.Extensions.Configuration;
 using YY.Admin.Core.Helper;
 using YY.Admin.Core.Session;
 using YY.Admin.FluentValidation;
+using YY.Admin.Helper;
 using YY.Admin.Services;
 using YY.Admin.Services.Service.Auth;
 using YY.Admin.Services.Service.Jeecg;
@@ -220,6 +221,31 @@ namespace YY.Admin.ViewModels
             while (!cancellationToken.IsCancellationRequested)
             {
                 bool connected = false;
+                var settings = ServerSettingsStore.Load();
+                if (settings.DisconnectConnection)
+                {
+                    try
+                    {
+                        await Application.Current.Dispatcher.InvokeAsync(() =>
+                        {
+                            IsBackendConnected = false;
+                        });
+                    }
+                    catch
+                    {
+                        // 忽略窗口关闭后的调度异常
+                    }
+
+                    try
+                    {
+                        await Task.Delay(TimeSpan.FromSeconds(ConnectivityCheckIntervalSeconds), cancellationToken);
+                    }
+                    catch (OperationCanceledException)
+                    {
+                        break;
+                    }
+                    continue;
+                }
                 try
                 {
                     // 每轮都重新读取配置，保存服务器设置后可即时生效
@@ -269,6 +295,11 @@ namespace YY.Admin.ViewModels
             {
                 if (r.Result == ButtonResult.OK)
                 {
+                    var settings = ServerSettingsStore.Load();
+                    if (settings.DisconnectConnection)
+                    {
+                        IsBackendConnected = false;
+                    }
                     LoginMessage = "服务器配置已保存";
                 }
             });