docs: add OpenZoo LLM provider guide

[staccDOTsol]

Updated 2026-09-02: corrected — the hosted https://api.openzoo.fun/v1 endpoint answers HTTP 402 to a plain OpenAI client (it only serves calls that pay x402 or carry an OpenZoo subscription key, ozk_live_…). The page now sets up the local npx openzoo proxy (http://localhost:8402/v1), which pays x402 per call from a local burner wallet and ignores the API key.

Your llms.mdx overview invites provider setup PRs from people who've run OpenHands against a provider — this adds a guide for OpenZoo: new page under openhands/usage/llms/, nav entry in docs.json, and a link in the llms.mdx provider list.

OpenZoo is OpenAI-compatible with no signup: a local npx openzoo proxy pays per call over x402 and ignores the API key, so the Advanced-settings table on the page is runnable as-is once the proxy is up (Custom Model openai/<id>, Base URL http://localhost:8402/v1, or http://host.docker.internal:8402/v1 from Docker). The model list at /v1/models is free to fetch. The hosted endpoint is mentioned only as needing x402 or a subscription key.

Disclosure: I operate OpenZoo.

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