Function checkpointTrustHeader

Adapt a checkpoint set into the synchronous core trustHeader hook, for verifiers that run offline. The check fires only when the claimed height is a checkpoint height: a mismatch is refused, a match asserts 'hash-at-height' exactly as makeHeaderTrust's checkpoint arm does, and every other height passes with no assertion, so the hook stays rejection-only where no checkpoint speaks. ord-resolve verify passes this hook on all three bundle kinds; heights the checkpoint set does not cover still rest on the reader's own chain view.