ci: validate Linux distributions and WSL2 support

[codeforester]

Summary

• run the full suite on both macOS and Ubuntu;
• add Debian 12 and Fedora latest Docker validation jobs;
• install the package in each distro environment and run the runtime smoke suite;
• document repeatable WSL2 validation and the limitations of Windows-mounted paths;
• add the Linux/WSL support guidance to the unreleased changelog.

Fixes #39

Validation

• uv run --no-project --with pytest --with click --with PyYAML python -m pytest
• ./tests/validate.sh
• workflow YAML parsed successfully

111 tests passed locally.