Add TitleBar to MAUI expert

[simonrozsival]

MAUI expert agent was struggling when I asked it to add TitleBar to my app. It attempted to add data templates to App.xaml resources instead of defining a new window, even when given link to the docs (https://learn.microsoft.com/en-us/dotnet/maui/user-interface/controls/titlebar?view=net-maui-10.0).