Summary:
- bump the package version to 0.4.2
- move the OTP 28.1 release workflow fix from Unreleased into the 0.4.2 changelog section
- update README installation guidance to the new release

Rationale:
- avoid rewriting the failed v0.4.1 tag
- publish the release workflow OTP floor fix in a clean follow-up patch release

Validation:
- mix compile --warnings-as-errors
- mix docs --warnings-as-errors --formatter html
- mix test --warnings-as-errors
- MIX_ENV=dev mix hex.publish --dry-run (package build succeeded; local publish blocked by missing Hex auth)

Co-authored-by: Codex <codex@openai.com>