PropsRecommendConversion

推荐带来的加购/下单。PRD 正文触发为「加购接口成功」；
action=order_paid 为标题中「下单」预留，规则需产品补充后启用。

{
    "action": "add_to_cart",
    "source_type": "recommendation",
    "item_id": "string",
    "quantity": 1,
    "unit_price": "string",
    "rec_session_id": "string"
}