fix: set ComboBox defaults from collection items (reference equality) (#38)

- Initialize Config.Platform/AppType from Platforms[0]/AppTypes[0] in VM
- Remove SelectedIndex=0 from XAML (conflicts with SelectedItem binding)
- Ensures selected item IS a collection item, not a separate instance

Author: JusterZhu

src/ViewModels/SimulateViewModel.cs

@@ -36,6 +36,8 @@ public partial class SimulateViewModel : ViewModelBase
     public SimulateViewModel()
     {
         _status = _loc["Patch.Ready"];
+        Config.Platform = Platforms[0];
+        Config.AppType = AppTypes[0];
     }
 
     async Task<string?> PickFolder(string title)

src/Views/SimulateView.axaml

@@ -38,12 +38,10 @@
                     <Grid ColumnDefinitions="Auto,*,Auto,*">
                         <TextBlock Grid.Column="0" Text="Platform" VerticalAlignment="Center"/>
                         <ComboBox Grid.Column="1" ItemsSource="{Binding Platforms}"
-                                  SelectedItem="{Binding Config.Platform}" Margin="8,0,16,0"
-                                  SelectedIndex="0"/>
+                                  SelectedItem="{Binding Config.Platform}" Margin="8,0,16,0"/>
                         <TextBlock Grid.Column="2" Text="AppType" VerticalAlignment="Center"/>
                         <ComboBox Grid.Column="3" ItemsSource="{Binding AppTypes}"
-                                  SelectedItem="{Binding Config.AppType}" Margin="8,0"
-                                  SelectedIndex="0"/>
+                                  SelectedItem="{Binding Config.AppType}" Margin="8,0"/>
                     </Grid>
                     <Grid ColumnDefinitions="Auto,*,Auto,*">
                         <TextBlock Grid.Column="0" Text="AppSecret" VerticalAlignment="Center"/>