feat: implement clean TDD-driven editor with enhanced status dialog

- Replace legacy editor with clean object-oriented architecture
- Add comprehensive test-driven Section, SectionManager, and DOMRenderer classes
- Implement four-layer content management with proper action semantics
- Add multiple concurrent section editing capability
- Implement intelligent section splitting with heading detection
- Add enhanced status dialog with repository info, version, and save filename
- Include git commit information and modification status
- Provide actual save filename preview instead of source filename
- Maintain proper section positioning and global reset functionality

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

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

markitect/cli.py

@@ -101,7 +101,7 @@ def detect_execution_mode():
 def should_use_associated_files():
     """Determine if commands should use associated files behavior."""
     return detect_execution_mode() == 'interactive'
-from .document_manager import DocumentManager
+# DocumentManager removed - using CleanDocumentManager directly in commands
 from .serializer import ASTSerializer
 from .cache_service import CacheDirectoryService
 from .ast_service import ASTService