Add isWaived() predicate: a waiver with a past 'expires' date is treated
as absent so the High/Critical advisory re-blocks. Applied in both
selectBlocking and partitionAdvisories. Add expired-waiver unit tests.
isMain now compares fully-resolved real paths (mirrors index.ts).
- Tests four behavioral cases: unwaived High → blocking, waived High → not blocking,
moderate/low only → not blocking, no advisories → not blocking
- Uses node:test + node:assert (no extra dependencies)
- Fails at RED: check-audit.mjs does not yet exist