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/main.py

@@ -0,0 +1,15 @@
+from fastapi import FastAPI
+
+from app.api import health, monitor, wechat_personal
+from app.config import settings
+
+app = FastAPI(title=settings.app_name, debug=settings.debug)
+
+app.include_router(health.router)
+app.include_router(wechat_personal.router)
+app.include_router(monitor.router)
+
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run("app.main:app", host=settings.host, port=settings.port, reload=settings.debug)