refactoring

Guides refactoring - restructuring code without changing its behavior - through characterization tests, small test-backed steps, Fowler's smell catalog, Tidy First, Mikado method, parallel change, branch by abstraction and strangler fig. Use when asked to refactor, restructure, clean up, split, rename, extract or untangle a function, module or legacy code, or to pay down tech debt; load it before proposing steps so each one names its smell and keeps tests green.