Prepare base-cli 0.4.1 release

[codeforester]

Summary

• bump the package and README release strip to 0.4.1
• move the post-0.4.0 changes into a dated 0.4.1 changelog section
• retain an Unreleased section for future work

Validation

• ./tests/validate.sh
• uv run pytest -q
• uv run ruff format --check lib/python/base_cli scripts examples tests
• uv run ruff check lib/python/base_cli scripts examples tests
• uv run mypy --strict examples/typed_consumer.py lib/python/base_cli
• uv run python scripts/validate_docs.py
• uv run python -m build --sdist --wheel
• uv run python scripts/validate_package_artifact.py
• uv run --with twine python -m twine check

Closes #170