Resolves #45220 (one of several PRs, we are very close) ## Testing - [X] QA'd all new/changed functionality manually <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit * **Tests** * Improved test infrastructure for the CLI: consolidated and renamed test helpers, added a dedicated in-process CLI test helper, and updated many test cases to use the new helpers. * Tightened several test assertions and standardized output/error validation across unit and integration tests to improve reliability. <!-- review_stack_entry_start --> [](https://app.coderabbit.ai/change-stack/fleetdm/fleet/pull/45585) <!-- review_stack_entry_end --> <!-- end of auto-generated comment: release notes by coderabbit.ai -->