fix: correct WebSocket message logging format

- Change format specifier from %s to %+v for struct logging
- Resolve compilation error in WebSocket message handling
- Maintain proper logging functionality for debugging

🤖 Generated with [Claude Code](https://claude.ai/code)

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

core/ws/ws.go

@@ -67,7 +67,7 @@ func Handler(w rest.ResponseWriter, r *rest.Request) {
 			continue
 		}
 
-		log.Printf("recv: %s", message)
+		log.Printf("recv: %+v", message)
 
 		// check version
 		err = checkVersion(message.Version)