modernize the sample app

It looks like the sample app still uses Angular v19. We should update to v20. There may be other updates we'd like to make during this process to more idiomatic patterns (e.g. get rid of environment file).

Locate the sample app's dependency configuration and Angular v19 references, then review the Angular v20 migration guidance before deciding which additional idiomatic updates are in scope. Done means the sample app runs on Angular v20, the agreed cleanup such as removing the environment file is complete, and the relevant checks pass.

Written by the indexing model from the issue text.