onboard: support custom provider in non-interactive flow (#14223)

Merged via /review-pr -> /prepare-pr -> /merge-pr.

Prepared head SHA: 5b98d6514e
Co-authored-by: ENCHIGO <38551565+ENCHIGO@users.noreply.github.com>
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Reviewed-by: @gumadeiras

docs/start/wizard-cli-automation.md

@@ -106,6 +106,23 @@ Add `--json` for a machine-readable summary.
       --gateway-bind loopback
     ```
   </Accordion>
+  <Accordion title="Custom provider example">
+    ```bash
+    openclaw onboard --non-interactive \
+      --mode local \
+      --auth-choice custom-api-key \
+      --custom-base-url "https://llm.example.com/v1" \
+      --custom-model-id "foo-large" \
+      --custom-api-key "$CUSTOM_API_KEY" \
+      --custom-provider-id "my-custom" \
+      --custom-compatibility anthropic \
+      --gateway-port 18789 \
+      --gateway-bind loopback
+    ```
+
+    `--custom-api-key` is optional. If omitted, onboarding checks `CUSTOM_API_KEY`.
+
+  </Accordion>
 </AccordionGroup>
 
 ## Add another agent