Add minimal 'steve' CLI package with tests, README, docs, and CI

[mataubertin]

Motivation

• Provide a tiny, testable Python CLI baseline for the steve project with no external dependencies.;
• Ensure tests are run automatically on pull requests and branch pushes via CI.;

Description

• Add a new steve package with a core function build_greeting in steve/__init__.py that returns deterministic greetings.;
• Add a CLI entrypoint steve/cli.py with a main function that prints the greeting and returns 0.;
• Add unit tests in tests/test_steve.py covering build_greeting behavior and main return code.;
• Update README.md, add docs/plan.md, and add a GitHub Actions workflow .github/workflows/ci.yml that runs python -m unittest discover -s tests -p 'test_*.py' on PRs and pushes to work, main, and master branches.;

Testing

• Run the unit test suite with python -m unittest discover -s tests -p 'test_*.py' and all tests passed.;
• Configure CI via .github/workflows/ci.yml to execute the same test command on pull requests and branch pushes.;
• No additional automated tests were added beyond the unit tests in tests/test_steve.py.

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Codex Task