docs: add Kunavo model provider guide

[cooldk]

Adds a provider guide for Kunavo under model-providers/more/, following the structure of the existing pages there (clawrouter.mdx as the template): OpenAI-compatible apiBase configuration in both YAML and deprecated-JSON forms, plus a short per-role model recommendation table. Also registers the page in docs.json navigation, alphabetically between groq and llamacpp.

Kunavo is a hosted OpenAI-compatible gateway serving Claude, Gemini and GPT models on one key — the guide uses Continue's standard openai provider with an apiBase override, so no code changes are involved.

Disclosure: I operate Kunavo.

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