Refactor — Expert Code Restructuring Surgical code refactoring based on Martin Fowler's <Refactoring (2nd Edition) catalog. Improve structure, readability, and maintainability without changing external behavior. Gradual evolution, not revolution. --- When to Use This skill activates when: - Code is hard to understand or maintain - Functions/classes have grown too large - Code smells are detected - Adding features is difficult due to poor structure - User explicitly requests refactoring, cleanup, or improvement - User says: refactor, 重构, clean up, improve code, code smell, extract method, rena…