Migrate to pyproject.toml with setuptools_scm

Replace custom version management with setuptools_scm to eliminate
source file modifications during installation. Version is now derived
from git tags at build time without writing to tracked files.

Changes:
- Add pyproject.toml with full project metadata
- Simplify setup.py to minimal backwards-compatible shim
- Remove curateipsum/_version.py from version control
- Add _version.py to .gitignore (auto-generated at build time)
- Use PEP 440 compliant version strings

Fixes #18

setup.py

@@ -1,48 +1,5 @@
-import setuptools
-import subprocess
+# Minimal setup.py for backwards compatibility
+# All configuration is in pyproject.toml
+from setuptools import setup
 
-
-def get_version_from_vcs():
-    ret_code, git_ver = subprocess.getstatusoutput("git describe")
-    if ret_code != 0:
-        from curateipsum._version import version
-        return version
-
-    with open("curateipsum/_version.py", "w") as fd:
-        fd.write("version = \"%s\"\n" % git_ver)
-        return git_ver
-
-
-with open("README.md", "r", encoding="utf-8") as fh:
-    long_description = fh.read()
-
-setuptools.setup(
-    name="cura-te-ipsum",
-    version=get_version_from_vcs(),
-    author="Maks Snegov",
-    author_email="snegov@spqr.link",
-    url="https://github.com/snegov/cura-te-ipsum",
-    description="Backup utility",
-    long_description=long_description,
-    long_description_content_type="text/markdown",
-    project_urls={
-        "Bug Tracker": "https://github.com/snegov/cura-te-ipsum/issues",
-        "GitHub": "https://github.com/snegov/cura-te-ipsum",
-    },
-    classifiers=[
-        "Development Status :: 2 - Pre-Alpha",
-        "Intended Audience :: Developers",
-        "Intended Audience :: System Administrators",
-        "License :: OSI Approved :: GNU General Public License v3 (GPLv3)",
-        "Operating System :: OS Independent",
-        "Programming Language :: Python :: 3",
-        "Topic :: System :: Archiving :: Backup",
-    ],
-    packages=setuptools.find_packages(include=["curateipsum"]),
-    entry_points={
-        "console_scripts": [
-            "cura-te-ipsum = curateipsum.cli:main",
-        ],
-    },
-    python_requires=">=3.6",
-)
+setup()