fix: polish opencode-zen onboarding (#623) (thanks @magimetal)

docs/start/wizard.md

@@ -77,6 +77,7 @@ Tip: `--json` does **not** imply non-interactive mode. Use `--non-interactive` (
    - **OpenAI Codex OAuth**: browser flow; paste the `code#state`.
      - Sets `agents.defaults.model` to `openai-codex/gpt-5.2` when model is unset or `openai/*`.
    - **OpenAI API key**: uses `OPENAI_API_KEY` if present or prompts for a key, then saves it to `~/.clawdbot/.env` so launchd can read it.
+   - **OpenCode Zen (multi-model proxy)**: prompts for `OPENCODE_ZEN_API_KEY` (get it at https://opencode.ai/auth).
    - **API key**: stores the key for you.
    - **MiniMax M2.1 (minimax.io)**: config is auto‑written for the OpenAI-compatible `/v1` endpoint.
    - **MiniMax API (platform.minimax.io)**: config is auto‑written for the Anthropic-compatible `/anthropic` endpoint.
@@ -185,6 +186,17 @@ clawdbot onboard --non-interactive \
   --gateway-bind loopback
 ```
 
+OpenCode Zen example:
+
+```bash
+clawdbot onboard --non-interactive \
+  --mode local \
+  --auth-choice opencode-zen \
+  --opencode-zen-api-key "$OPENCODE_ZEN_API_KEY" \
+  --gateway-port 18789 \
+  --gateway-bind loopback
+```
+
 Add agent (non‑interactive) example:
 
 ```bash