feat: add Micu API as sponsor and update affiliate links

Add Micu (米醋API) sponsor entry to all three README files (EN/ZH/JA)
with logo and description. Update apiKeyUrl for Micu provider presets
across claude, codex, opencode, and openclaw to use affiliate
registration link.

README.md

@@ -80,6 +80,11 @@ Claude Code / Codex / Gemini official channels at 38% / 2% / 9% of original pric
 <td>Thanks to SSSAiCode for sponsoring this project! SSSAiCode is a stable and reliable API relay service, dedicated to providing stable, reliable, and affordable Claude and Codex model services, <strong>offering high cost-effective official Claude service at just ¥0.5/$ equivalent</strong>, supporting monthly and pay-as-you-go billing plans with same-day fast invoicing. SSSAiCode offers a special deal for CC Switch users: register via <a href="https://www.sssaicode.com/register?ref=DCP0SM">this link</a> to enjoy $10 extra credit on every top-up!</td>
 </tr>
 
+<tr>
+<td width="180"><a href="https://www.openclaudecode.cn/register?aff=aOYQ"><img src="assets/partners/logos/mikubanner.svg" alt="Micu" width="150"></a></td>
+<td>Thanks to Micu API for sponsoring this project! Micu API is a global LLM relay service provider dedicated to delivering the best cost-performance ratio with high stability. Backed by a registered enterprise for core assurance, eliminating any risk of service discontinuation, with fast official invoicing support! We champion "zero cost to try": top up from as low as ¥1 with no minimum, and get fee-free refunds anytime! Micu API offers an exclusive deal for CC Switch users: register via <a href="https://www.openclaudecode.cn/register?aff=aOYQ">this link</a> and enter promo code "ccswitch" when topping up to enjoy a <strong>10% discount</strong>!</td>
+</tr>
+
 </table>
 
 </details>