feat: added some filed to shipment serializers

docs/api_v2_agent_api.md

@@ -45,6 +45,8 @@ Authorization: <AGENT_ACCESS_KEY>
   "merchant_id": 10,
   "customer": 5,
   "customer_name": "客户A",
+  "fabric": "棉布 40S",
+  "order_description": "订单备注",
   "shipment_date": "2026-04-14",
   "address": "广州市天河区",
   "contact_name": "张三",
@@ -154,6 +156,8 @@ Authorization: <AGENT_ACCESS_KEY>
 
 - "未出货"定义：`delivery` 为空，即尚未关联送货单
 - `delivery_id` 始终返回送货单ID；未关联时为 `null`
+- `fabric` 来自该出货单所关联销售品对应生产订单的 `fabric`；若当前出货单没有销售品则返回 `null`
+- `order_description` 来自该出货单所关联销售品对应生产订单的 `description`；若当前出货单没有销售品则返回 `null`
 - 结果按 `created_at` 降序排列
 - 只返回 `merchant_id` 对应商户的数据
 - `sales_items` 包含该出货单的所有销售品（软删除的条目自动排除）