docs: add Privnode sponsor advertisement to README

Add Privnode as a sponsor with 15% discount code WITHCCH.
Updated both Chinese and English README files.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

README.en.md

@@ -36,6 +36,20 @@ Cubence offers special discount coupons for users of CCH: when purchasing with t
 </tr>
 </table>
 
+<table>
+<tr>
+<td width="200">
+<a href="https://privnode.com/with-cch?utm_source=refLink">
+<img src="public/readme/privnode.png" alt="Privnode Logo" width="180"/>
+</a>
+</td>
+<td>
+<b>💎 Special Offer</b>: <a href="https://privnode.com/with-cch?utm_source=refLink">Privnode</a> is an affordable AI API aggregation platform providing one-stop relay services for mainstream models like Claude and Codex, serving developers and teams with reliable stability and competitive pricing.<br/>
+Use code <code>WITHCCH</code> for <b>15% off</b> → <a href="https://privnode.com/with-cch?utm_source=refLink">Visit Now</a>
+</td>
+</tr>
+</table>
+
 ## ✨ Core Highlights
 
 - 🤖 **Intelligent load balancing**: Weight + priority + grouping scheduler with built-in circuit breaker and up to three failover retries to keep requests stable.

README.md

@@ -36,6 +36,20 @@ Cubence 为 CCH 的使用用户提供了特别的优惠折扣：在购买时使
 </tr>
 </table>
 
+<table>
+<tr>
+<td width="200">
+<a href="https://privnode.com/with-cch?utm_source=refLink">
+<img src="public/readme/privnode.png" alt="Privnode Logo" width="180"/>
+</a>
+</td>
+<td>
+<b>💎 特别优惠</b>：<a href="https://privnode.com/with-cch?utm_source=refLink">Privnode</a> 是一家平价的 AI API 聚合平台，为 Claude、Codex 等主流模型提供一站式中转服务，以良好的稳定性和较高的性价比，服务于开发者与团队的实际需求。<br/>
+使用优惠码 <code>WITHCCH</code> 可获得 <b>15% 折扣</b> → <a href="https://privnode.com/with-cch?utm_source=refLink">立即访问</a>
+</td>
+</tr>
+</table>
+
 ## ✨ 核心功能 Highlights
 
 - 🤖 **智能负载均衡**：权重 + 优先级 + 分组调度，内置熔断保护与最多 3 次故障转移，保障请求稳定。