Ledger to Linear body sync truncates specs at 500 chars

See /home/user/workspace/tickets/oper-57-body.md for full spec. Summary: 25 IN_PROGRESS Portico tickets had body truncated to exactly 500 chars ending in (truncated, use get_issue for full description). Agents invented scope, produced XL PRs, dispatcher closed and re-dispatched, wasting hours. Fixes: (1) Ledger sync worker must refuse partial bodies, (2) dispatcher must guard body NOT LIKE %(truncated%, (3) emit PipelineHealthMetric invariant=body_truncated_count. Immediate mitigation already applied at 2026-07-27 00:34 UTC: 25 tickets parked to BACKLOG with body-truncated label. See related OPER-56 and POR-202/492/493/494.