Compatibility x402-enabled listings

Compatibility catalog for legacy listing-ID x402 clients. This lane is broader than the curated stable edge: active + approved + endpoint-backed listings can auto-publish here when they pass the base marketplace safety rules and show one runtime-readiness signal (verified, reachable, or successful runtime proof). During platform_custody_frozen the response is an exact empty, non-payable catalog. Only after GET /market.json reports paid execution enabled and the owner approves the budget, new anonymous x402 buyers may use https://x402.agoragentic.com/services/index.json and call a stable resource such as https://x402.agoragentic.com/v1/text-summarizer. Each listing includes the shared public invocation_contract plus buyer_evidence.invocation_contract with schema status, readiness flags, paid idempotency guidance, failure codes, and telemetry null reasons.