docs: use Volcengine logo for Chinese README sponsor entry

Replace byteplus.png with localized huoshan.png (Volcengine/火山引擎)
in README_ZH.md so Chinese readers see the regional brand. EN/JA
README continue to use the BytePlus logo and link to byteplus.com.

The new logo is normalized to the project's standard sponsor image
spec: 1920x798 RGB on a white background.

README_ZH.md

@@ -60,7 +60,7 @@ Claude Code / Codex / Gemini 官方渠道低至 3.8 / 0.2 / 0.9 折，充值更
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 <tr>
-<td width="180"><a href="https://www.volcengine.com/activity/agentplan?utm_campaign=hw&utm_content=ccswitch&utm_medium=devrel_tool_web&utm_source=OWO&utm_term=ccswitch"><img src="assets/partners/logos/byteplus.png" alt="BytePlus" width="150"></a></td>
+<td width="180"><a href="https://www.volcengine.com/activity/agentplan?utm_campaign=hw&utm_content=ccswitch&utm_medium=devrel_tool_web&utm_source=OWO&utm_term=ccswitch"><img src="assets/partners/logos/huoshan.png" alt="HuoShan" width="150"></a></td>
 <td>感谢火山方舟Agent Plan 模型赞助了本项目！方舟Agent Plan 模型订阅套餐集成了包含Doubao-Seed、Doubao-Seedance、Doubao-Seedream等在内的字节跳动自研SOTA级模型，覆盖文本、代码、图像、视频等多模态任务。同时支持一站式接入DeepSeek V4、GLM 5.1等主流大模型。超全模态模型与 Harness 升级一步到位，深度支持 Agent 框架与 AI 编程工具。方舟 Agent Plan 为 CC Switch 的用户提供了专属福利：通过<a href="https://www.volcengine.com/activity/agentplan?utm_campaign=hw&utm_content=ccswitch&utm_medium=devrel_tool_web&utm_source=OWO&utm_term=ccswitch">此链接</a>订阅方舟AgentPlan，新客户首月40元起！</td>
 </tr>