添加使用火山coding plain配置参数

[gphper]

📝 Description

使用火山引擎的coding plain时需要配置
"api_base":"https://ark.cn-beijing.volces.com/api/coding/v3"
参考文档在这里
火山引擎coding plain使用手册

[CLAassistant]

All committers have signed the CLA.

[yinwm]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

This is a straightforward documentation update that adds the required api_base parameter for Volcano Engine (火山引擎) Coding Plain configuration across all README language versions. The JSON syntax is correct and the endpoint URL looks valid.

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[yinwm]

LGTM

[Orgmar]

@gphper 火山引擎coding plan的配置补充得很及时，api_base指向coding/v3端点这个细节容易被忽略，有了文档引用也方便其他用户参考。

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