Add designer file menu and package metadata

LehrerApp.TemplateDesigner/StarterTemplateLibrary.cs

@@ -108,6 +108,8 @@ public sealed class StarterTemplateLibrary
         Description = source.Description,
         PageSize = new(source.PageSize.Width, source.PageSize.Height, source.PageSize.Unit),
         LayoutFile = source.LayoutFile,
+        MetadataFile = source.MetadataFile,
+        Metadata = new(source.Metadata, StringComparer.OrdinalIgnoreCase),
         Placeholders = source.Placeholders.Select(x => new PlaceholderDefinition(x.Name, x.Type, x.Required)).ToList(),
     };