feat(channel): add mci-channel-wechat-personal adapter

- New module: mci-channel-wechat-personal
- Implements ChannelAdapter SPI for personal WeChat
- Calls Python channel-service pywechat HTTP APIs:
  - /v1/wechat-personal/login/start for initAccount QR code
  - /v1/wechat-personal/send/text and /send/image for sendMessage
- Configurable base URL via sino.channel.wechat-personal.base-url
- Added MockWebServer unit tests
- Wired module into backend parent and mci-server

backend/mci-server/pom.xml

@@ -24,6 +24,10 @@
             <groupId>com.sino</groupId>
             <artifactId>mci-channel-wecom</artifactId>
         </dependency>
+        <dependency>
+            <groupId>com.sino</groupId>
+            <artifactId>mci-channel-wechat-personal</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-web</artifactId>