[HoungDev]

What changed

• add installed creator-toolkit entrypoint smoke tests for help, JSON output, rename preview, and error handling
• run the smoke suite on Ubuntu, macOS, and Windows with Python 3.12
• document the supported operating systems and CI support policy
• mark the package as operating-system independent

Why

Unit tests already cover the application logic, but they do not prove that the built package exposes a working console command on each supported operating system. This PR adds a focused installed-package gate without duplicating the full unit-test matrix.

Impact

Contributors get fast, explicit feedback when packaging or cross-platform behavior breaks. Users get a documented support policy for current Windows, macOS, and Linux releases.

Validation

• ruff check .
• ruff format --check .
• pytest — 48 passed, 93.79% coverage
• installed CLI smoke suite — 4 passed
• GitHub Actions workflow YAML parse
• wheel and source distribution build
• twine check
• source distribution contents verified for platform support docs
• pip-audit — no known vulnerabilities in third-party dependencies
• pip check

Closes #5