docs: document public API annotations

[marandaneto]

💡 Motivation and Context

Keep the SDK's public API documentation annotations complete and avoid stale Rails usage examples in the package README. Public methods/configuration now have YARD annotations for parameters, options, return values, deprecations, and experimental/private status where appropriate.

💚 How did you test it?

• bundle exec rubocop
• bundle exec rspec

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran pnpm changeset to generate a changeset file