pr-retro

Use when the user asks for a branch retrospective, pre-PR analysis, branch health check, or says "/pr-retro". Analyzes all commits on the current branch vs base (main..HEAD), computes size metrics, test LOC ratio, focus score, session analysis, commit hygiene, contributor breakdown, self-review scan (TODOs, debug artifacts, .only, secrets), and delivers a merge readiness verdict (GREEN/YELLOW/RED). Supports --quick…