fix: serialize datetime objects in agent dict before JSON encoding in create_agent_execution

dashboard/backend/db/opc_db.py

@@ -543,9 +543,14 @@ async def create_agent_execution(
             if task_for_context.get(key):
                 task_for_context[key] = task_for_context[key].isoformat() if hasattr(task_for_context[key], 'isoformat') else task_for_context[key]
 
+        agent_for_context = dict(agent)
+        for key in ["created_at"]:
+            if agent_for_context.get(key):
+                agent_for_context[key] = agent_for_context[key].isoformat() if hasattr(agent_for_context[key], 'isoformat') else agent_for_context[key]
+
         input_context = {
             "task": task_for_context,
-            "agent": dict(agent),
+            "agent": agent_for_context,
             "timestamp": datetime.utcnow().isoformat()
         }