release: prepare v0.4.0 - Enhanced Edit Mode & Version Tracking

Key improvements:
- Fixed critical md-render --edit functionality that was broken
- Enhanced version tracking with git commit hash, timestamps, and local changes detection
- Comprehensive regression tests to prevent future breaks
- Repository cleanup completed

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

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

markitect/__version__.py

@@ -11,7 +11,7 @@ from pathlib import Path
 from typing import Optional
 
 # Base version from pyproject.toml
-__version__ = "0.3.0"
+__version__ = "0.4.0"
 
 def get_git_commit_hash() -> Optional[str]:
     """Get the current git commit hash if available."""