fix: 登录窗口可调整大小，修复异步警告

- 登录窗口支持调整大小（最小400x300，最大600x500）
- 修复BatchShipSelected方法的CS1998异步警告

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PackagingMallShipper/ViewModels/OrderListViewModel.cs

@@ -250,7 +250,7 @@ namespace PackagingMallShipper.ViewModels
         }
 
         [RelayCommand]
-        private async Task BatchShipSelectedAsync()
+        private void BatchShipSelected()
         {
             var selectedOrders = Orders.Where(o => o.IsSelected && o.Status == 1).ToList();
             if (!selectedOrders.Any())

PackagingMallShipper/Views/LoginWindow.xaml

@@ -5,9 +5,11 @@
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         mc:Ignorable="d"
         Title="包装商城发货助手 - 登录"
-        Height="480" Width="350"
+        Height="500" Width="350"
+        MinHeight="400" MinWidth="300"
+        MaxHeight="600" MaxWidth="500"
         WindowStartupLocation="CenterScreen"
-        ResizeMode="NoResize"
+        ResizeMode="CanResizeWithGrip"
         Background="#F5F5F5">
     
     <Grid>