fix: convert datetime objects to ISO strings before JSON serialization in task history

dashboard/backend/db/opc_db.py

@@ -258,11 +258,17 @@ async def create_task(
         task = dict(row)
         task["tags"] = json.loads(task["tags"]) if task["tags"] else []
 
+        # Convert datetime objects to ISO format strings for JSON serialization
+        task_for_history = task.copy()
+        for key in ["created_at", "updated_at", "completed_at", "due_date"]:
+            if task_for_history.get(key):
+                task_for_history[key] = task_for_history[key].isoformat()
+
         # Log history
         await conn.execute("""
             INSERT INTO task_history (task_id, action, actor, actor_type, new_value)
             VALUES ($1, $2, $3, $4, $5)
-        """, task["id"], "created", actor, "human", json.dumps(task))
+        """, task["id"], "created", actor, "human", json.dumps(task_for_history))
 
         return task