Clarify ViewModel lifecycle & disposal in Compass sample

[Turskyi]

In the Compass sample, HomeViewModel (a ChangeNotifier) is created in the router and passed into HomeScreen, but it is never disposed.

While this is currently safe because HomeViewModel does not manage any disposable resources, this pattern may be confusing for readers who copy it into real apps where ViewModels often own streams, subscriptions, or controllers.

Would it make sense to:
• Add a short comment explaining that the ViewModel currently does not require disposal, and
• Clarify that lifecycle ownership would need to be addressed if disposable resources are introduced (e.g. via Provider/Riverpod or a StatefulWidget)?

This could help prevent accidental memory leaks when developers adapt the pattern.