fix(gateway): remove double-reverse of history messages in _send_to_agent_background

hist_msgs is already sorted oldest→newest by list(reversed(...)), so
passing reversed(hist_msgs) to _conv() flips the order again, causing
the model to read conversation history in reverse chronological order.

Author: ThomasOscar

backend/app/api/gateway.py

@@ -390,7 +390,7 @@ async def _send_to_agent_background(
             hist_msgs = list(reversed(hist_result.scalars().all()))
 
             from app.services.llm.utils import convert_chat_messages_to_llm_format as _conv
-            messages = _conv(reversed(hist_msgs))
+            messages = _conv(hist_msgs)
 
             # Add the new message with agent communication context
             user_msg = f"{agent_comm_alert}\n\n[Message from agent: {source_agent_name}]\n{content}"