Add OpenCode Go provider docs page

[zoomote]

Context

Zoo Code ships an OpenCode Go provider (opencode-go) — the OpenCode Go plan's curated model catalog (GLM, Kimi, MiMo, DeepSeek, Qwen, MiniMax) with a dynamic model picker and per-model wire-format routing (Anthropic-format vs OpenAI-compatible). Unlike most other providers, it has no documentation page in docs/providers/, and it is not registered in docs/providers/index.json.

Related code references:

• Registry: packages/types/src/providers/opencode-go.ts in Zoo-Code
• Settings UI: webview-ui/src/components/settings/providers/OpenCodeGo.tsx
• Recent model addition (Kimi K3): Zoo-Code #996

Ask

Add docs/providers/opencode-go.md following the existing provider-page template (getting a key/plan, configuration steps, available models or link to the model picker, wire-format notes) and register it in docs/providers/index.json so it appears in the Model Providers sidebar and comparison table.

Notes

• Follow the same structure as docs/providers/moonshot.md and the Kimi Code page in PR #17.
• Mention that model capability flags (reasoning effort, prompt caching, image support) are curated per model in the registry.