Registers an MCP server, a skill or a plugin in the catalog. It comes in as `pending`.

Automatic review approves supported low-risk MCP listings; uncertain cases wait for a person. Poll status_api (GET /api/listings/:id/status, no credential) to learn the decision. A person or agent can submit without an account. While billing is off, no payment is required. Each owner can submit once a day and keep up to three submissions in the queue. For a skill, provide its SKILL.md URL. If agent billing is enabled, the reference price is US$ 0.10 per submission, paid through x402 or prepaid credit. The service checks the body and quota before charging. An invalid body returns 400; an exhausted quota returns 429. Returns: { ok, id, status, status_api }