fix: set sender for internal messages

ref: N25B-441

src/control_backend/core/agent_system.py

@@ -133,6 +133,7 @@ class BaseAgent(ABC):
 
         :param message: The message to send.
         """
+        message.sender = self.name
         to = message.to
         receivers = [to] if isinstance(to, str) else to