Update appmodel.md

[davidfowl]

Update the talking clock example

[Copilot]

Pull Request Overview

This PR updates the talking clock example in the Aspire documentation to demonstrate a more comprehensive custom resource implementation with parent-child relationships and improved event handling patterns.

• Refactors the talking clock example to use the newer OnInitializeResource event pattern instead of lifecycle hooks
• Introduces clock hand sub-resources with parent-child relationships to show hierarchical resource modeling
• Updates state management to demonstrate coordinated state updates across multiple related resources

[davidfowl]

@joperezr @radical why is this stuck