refactor: use options object pattern for JsonlToMarkdownConverter

- Add ConverterOptions interface for better extensibility
- Replace individual constructor parameters with options object
- Update all internal references to use this.options
- Make version dynamic by reading from package.json
- Add --output CLI option to specify custom output directory

This refactoring makes it easier to add new options in the future without
breaking the API or requiring changes to constructor signatures.

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Co-Authored-By: Claude <noreply@anthropic.com>