docs: add USB port warning to prevent plugging into wrong port

Many ESP32-S3 boards have two USB-C ports (USB and COM). Added a
callout with a reference photo reminding users to use the USB
(Serial/JTAG) port instead of the COM (UART bridge) port.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -85,6 +85,15 @@ ls /dev/ttyACM*          # Linux
 idf.py -p PORT flash monitor
 ```
 
+> **Important: Plug into the correct USB port!** Most ESP32-S3 boards have two USB-C ports. You must use the one labeled **USB** (native USB Serial/JTAG), **not** the one labeled **COM** (external UART bridge). Plugging into the wrong port will cause flash/monitor failures.
+>
+> <details>
+> <summary>Show reference photo</summary>
+>
+> <img src="assets/esp32s3-usb-port.jpg" alt="Plug into the USB port, not COM" width="480" />
+>
+> </details>
+
 ### CLI Commands
 
 Connect via serial to configure or debug. **Config commands** let you change settings without recompiling — just plug in a USB cable anywhere.

README_CN.md

@@ -85,6 +85,15 @@ ls /dev/ttyACM*          # Linux
 idf.py -p PORT flash monitor
 ```
 
+> **注意：请插对 USB 口！** 大多数 ESP32-S3 开发板有两个 Type-C 接口，必须插标有 **USB** 的那个口（原生 USB Serial/JTAG），**不要**插标有 **COM** 的口（外部 UART 桥接）。插错口会导致烧录/监控失败。
+>
+> <details>
+> <summary>查看参考图片</summary>
+>
+> <img src="assets/esp32s3-usb-port.jpg" alt="请插 USB 口，不要插 COM 口" width="480" />
+>
+> </details>
+
 ### 代理配置（国内用户）
 
 在国内需要代理才能访问 Telegram 和 Anthropic API。MimiClaw 内置 HTTP CONNECT 隧道支持。