Add LICENSE, fix PEP 639 classifier warning, enhance --version output, add dev dependencies

- Create MIT LICENSE file
- Remove deprecated License classifier, add license-files to pyproject.toml
- Add __license__ constant to __init__.py
- Show full name, copyright, and license in rp --version
- Add ruff and mypy as dev dependencies

src/rp/cli.py

@@ -9,7 +9,7 @@ from typing import Annotated, Optional
 import typer
 from rich.console import Console
 
-from rp import __version__
+from rp import __author__, __license__, __version__
 from rp.detect import detect_type
 from rp.render import RenderOptions, render
 
@@ -24,7 +24,9 @@ app = typer.Typer(
 def version_callback(value: bool) -> None:
     if value:
         console = Console()
-        console.print(f"rp {__version__}")
+        console.print(f"Rich Print (rp) {__version__}")
+        console.print(f"Copyright (c) 2026 {__author__}")
+        console.print(f"License: {__license__}")
         raise typer.Exit()