Gitnexus Refactoring

This handles the hard part of refactoring: tracking down every place a symbol is used before you rename or move it. It maps dependencies with gitnexus_impact, then runs automated renames across multiple files with confidence scoring (graph-based edits are safe, AST search results need review). The workflow is structured around impact analysis first, then execution, then verification with detect_changes to see what you actually touched. Most useful when you're renaming something with more than five callers or extracting code that's referenced across different areas of the codebase. The dry run mode is smart since you can preview edits before committing to them.