Pipeline self-heal Phase B: auto-heal ghost IN_PROGRESS tasks

Ships AFTER 24h of clean OPER-7A signal. DOC-approved guardrails required:
1. Double-check before revert (30s apart) to defeat transient GitHub 500s
2. Rate-limit: max 20 auto-heals per 5-min window per team
3. Circuit-breaker: 3 consecutive violations disables auto-heal, alerts human
4. TaskAutoHealed audit event with full pre-heal snapshot for rollback
5. Emits SEV-3 Slack on every heal, SEV-2 on circuit-breaker trip

Blocked by: OPER-7A merge + 24h observation window.