Cover base_dev artifact checks

[codeforester]

Summary

• Add direct unit coverage for base_dev Homebrew artifact checks across installed, missing, missing Homebrew, unsupported version, and unsupported manager states.
• Add non-dry-run setup_dev_artifacts coverage for successful reconciliation and per-artifact failure reporting.
• Add GitHub CLI auth coverage for missing gh, unauthenticated gh, and authenticated gh, and return structured findings when brew or gh are missing from PATH.

Validation

• env PYTHONPATH=lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_dev/tests/test_engine.py
• env -u BASE_HOME HOME=/private/tmp/base-review-home BASE_TEST_PYTHON=/Users/rameshhp/.base.d/base/.venv/bin/python bin/base-test
• git diff --check

Closes #300