Add setup.py shim for tools that require it

Most build-time tools use pyproject.toml directly, but some legacy
documentation generators look for setup.py. The shim reads version
from VERSION.txt or PackageVersion env var for build pipelines.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Abel Milash

setup.py

@@ -0,0 +1,14 @@
+from os import environ, path
+from setuptools import setup
+
+# Try to read from VERSION.txt file first, fall back to environment variable
+version_file = path.join(path.dirname(__file__), "VERSION.txt")
+if path.exists(version_file):
+    with open(version_file, "r", encoding="utf-8") as f:
+        package_version = f.read().strip()
+else:
+    package_version = environ.get("PackageVersion", "0.0.0")
+
+setup(
+    version=package_version,
+)