feat(channel-service): add Python FastAPI pywechat channel service

- Add FastAPI project under channel-service/
- Implement mock pywechat client adapter (login, send, heartbeat)
- Add /v1/wechat-personal/login/*, /v1/wechat-personal/send/* APIs
- Add /v1/heartbeat and /v1/monitor/status for client health
- Add /monitor HTML page with Web Components
- Add pytest suite and Dockerfile
- Update .gitignore for Python/Node artifacts

channel-service/app/api/health.py

@@ -0,0 +1,8 @@
+from fastapi import APIRouter
+
+router = APIRouter(tags=["health"])
+
+
+@router.get("/health")
+def health_check():
+    return {"status": "ok", "service": "sino-mci-channel-service"}