Complete six-language documentation and release parity

[nicklambourne]

Summary

• Add RubyGems and Ruby CI badges, installation, notification example, and contributor guidance to the root README.
• Bring current contributing, installation, troubleshooting, spec, release, and package READMEs up to date for all six language packages. Preserve historical ADR and versioned documentation context.
• Add a Ruby executable documentation example tested against the shared JSON fixture.
• Include the Ruby version in the version guards of the five existing publisher workflows, matching the coordinator and Ruby publisher.

Verification

• Ruby 3.3 suite: 419 tests, 1598 assertions; new executable docs example: 1 test, 2 assertions.
• Ruby StandardRB on the new example and test.
• Docs language content, Ruby guide snippets, guide previews, release snapshots, and TypeScript typecheck.
• actionlint on all five modified publisher workflows; version extraction and mismatch rejection checked locally.
• git diff --check.

The full docs build requires JDK and .NET, which are not installed on the local host; PR CI will run that build on GitHub-hosted runners.