Verify `dotnetup list` shows dependent shared frameworks when ASP.NET/WindowsDesktop runtime is installed

## Summary

As discussed in https://github.com/dotnet/sdk/pull/52717#discussion_r2755556195, we need to ensure `dotnetup list` correctly handles scenarios where different shared frameworks are installed.

## Scenarios to Test

1. **Only core runtime installed** - Should show only `Microsoft.NETCore.App`
2. **ASP.NET runtime installed** - Should show both `Microsoft.AspNetCore.App` AND `Microsoft.NETCore.App` (since ASP.NET depends on the core runtime)
3. **Windows Desktop runtime installed** - Should show both `Microsoft.WindowsDesktop.App` AND `Microsoft.NETCore.App`
4. **Multiple runtimes** - All installed shared frameworks should be listed

## Verification Needed

The manifest itself might not be tracking the core runtime dependency explicitly when higher-level runtimes are installed. We need to verify:

1. When installing ASP.NET runtime, the manifest records both ASP.NET and the core runtime
2. The `list` command shows all dependent runtimes, not just the explicitly requested one

## Notes

Runtime install support is not yet in the PR branch (#52717), so this needs to be tracked separately and verified when runtime installs are implemented.

## Related

- PR: #52717
- Future: Runtime install support for dotnetup