Fix pending Live Cast tasks backfill

Why is every task pending Live Cast?? Fix it asap and backfill 

Cause: a deploy orphaned Live Cast's run, which still holds the project's dedup key, so every task stayed Pending. Fix: cp_ecs recovers workflows of tasks that vanished from ECS, and the sweep cancels stuck runs. PR #6674 merged and the dev deploy is green (30 orphans recovered). Prod backfills after promotion. Draft follow-up #9136. Memory: proposed 1 gotcha.