dc validation triage

Real MMUCC6 Edit Rule violations against dc's mapped sample data - the human-decision step CLAUDE.md's "Validation-error triage" locks in: every violation needs a real fix/exclude/delete/allow decision before export, never a silent pass-through. Decisions save to a real file (triage-decisions/dc.json) and reload here on your next visit. Honest MVP boundary: this still isn't the export gate - nothing downstream reads these decisions yet.