- Add app list-users subcommand to get users for specific apps

- Add comprehensive tests for app functionality

- Refactor mock client to utils package for better reusability

- Add GetAppsDetails method to retrieve apps with user information

- Introduce AppDetails struct to combine app and user data

- Add --detail flag to app list command for enhanced output

- Include comprehensive test coverage for new functionality

- Handle user fetch errors gracefully by setting empty user slice