Implement rp CLI: rich-print markdown, JSON, code, and more

- Add typer CLI with auto file-type detection by extension
- Support markdown (rich.Markdown), JSON (rich.JSON), and 30+ code
  languages via Pygments syntax highlighting
- Features: line numbers toggle, pager support, stdin input,
  configurable color themes
- Project metadata: MIT license, author, classifiers, entry point

README.md

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+# rp
+
+Rich print files — markdown, JSON, code, and more — beautifully in your terminal.