Prepare v0.2.1 release

[polishdataengineer]

What changed

• bumps the package, lockfile, and source-checkout fallback version from 0.2.0 to 0.2.1
• releases the compact native terminal reporter entries from Unreleased in the changelog
• updates README and documentation now that Testenix is already available on PyPI
• replaces stale hard-coded 0.1 LLM guidance with version-independent wording
• regenerates both complete LLM documentation snapshots

Why

The compact terminal output merged after v0.2.0 is currently available only from main. The release workflow requires an exact v0.2.1 tag/package-version match and requires the tagged commit to belong to protected main.

User impact

After the GitHub Release and trusted PyPI publication complete, users can install testenix==0.2.1 and receive the new compact per-file terminal UI plus the new console flags. Structured JSON/JUnit output, pytest bridge behavior, result semantics, and exit codes remain unchanged.

Validation

• 333 passed with pytest
• 333 passed through testenix pytest -q
• Ruff check and format: clean
• mypy: clean
• pyright: 0 errors
• docs assets reproducible on Python 3.11 and the local runtime
• Sphinx 9.0.4 / Python 3.11 with -W: clean
• wheel and sdist built as 0.2.1
• Twine strict and check-wheel-contents: clean
• isolated wheel and sdist report Testenix 0.2.1 and pass the native example smoke test
• pytest extra from the wheel resolves and runs

The unrelated local .gitignore change is not included.