Verify an x402 endpoint and decide whether it is ready to publish

Run a free point-in-time readiness scan before an agent pays or a provider publishes. The response includes signed evidence plus an unsigned, grade-aware provider listing handoff: ready endpoints can validate metadata free before optionally buying the 0.50 USDC publication; non-ready endpoints are told to fix and re-verify before paying. Publication never buys readiness, ranking, traffic, leads, purchases, or safety.