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

pyproject.toml

@@ -4,6 +4,7 @@ version = "0.2.0"
 description = "Rich print files — markdown, JSON, code, and more — beautifully in your terminal"
 readme = "README.md"
 license = "MIT"
+license-files = ["LICENSE"]
 authors = [
     { name = "Yunxiao Xu", email = "xuyunxiao2001@gmail.com" }
 ]
@@ -12,7 +13,6 @@ classifiers = [
     "Development Status :: 4 - Beta",
     "Environment :: Console",
     "Intended Audience :: Developers",
-    "License :: OSI Approved :: MIT License",
     "Programming Language :: Python :: 3",
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
@@ -32,6 +32,12 @@ rp = "rp.cli:app"
 Homepage = "https://github.com/yunxiaoxu/rich-viewer"
 Repository = "https://github.com/yunxiaoxu/rich-viewer"
 
+[dependency-groups]
+dev = [
+    "ruff>=0.9",
+    "mypy>=1.14",
+]
+
 [build-system]
 requires = ["uv_build>=0.11.2,<0.12.0"]
 build-backend = "uv_build"