modularize

One focused, repeatable pass that retires the code-quality scorecard's architecture debt — the god-files (>1500 lines) and god-functions (>200 lines) that /quality-score flags as RISKY and explicitly defers to "a focused pass". Splits a monolith along REAL concern seams via behavior-preserving code motion (the goimports recipe: hazard-check → plan boundaries with tools/godsplit_plan.py → sed-extract → goimports -w →…