Convert to setuptools-scm for automatic version management

- Remove manual version management in favor of git tag-based versioning
- Simplify __version__.py to import from generated _version.py
- Add simplified release_simplified.py script
- Add _version.py to .gitignore (auto-generated)

🚀 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitignore

@@ -96,3 +96,4 @@ ISSUES.index
 
 # Test artifacts and temporary files
 tmp/
+markitect/_version.py