fix: 消息通知页不能点进详情 — 补全 product_serial_number

问题: 点击通知卡片跳转 detail?taskId=xxx，但 detail.vue onLoad 只认 serial 参数导致空白页

修复:
1. 后端 NotificationResponse 新增 product_serial_number 字段
2. 后端 notifications API 联表 tasks+products 批量填充 serial
3. 前端 notify/index.vue handleCardTap 优先用 product_serial_number 跳转，兜底从 content 正则解析
4. 前端 detail.vue onLoad 新增 taskId 兜底 → doQueryByTask 反查 product_sn

backend/app/api/v1/endpoints/notifications.py

@@ -4,9 +4,12 @@ import uuid
 from fastapi import APIRouter, Depends, Query
 from sqlalchemy import select, func
 from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
 
 from app.core.database import get_db
 from app.models.notification import Notification
+from app.models.task import Task
+from app.models.product import Product
 from app.schemas.notification import NotificationResponse, NotificationListResponse
 
 router = APIRouter(prefix="/notifications", tags=["消息通知"])
@@ -46,10 +49,28 @@ async def list_notifications(
     result = await db.execute(stmt)
     notifications = result.scalars().all()
 
+    # 🚀 批量查询关联的 product_serial_number
+    task_ids = [n.task_id for n in notifications if n.task_id]
+    serial_map: dict[uuid.UUID, str] = {}
+    if task_ids:
+        task_result = await db.execute(
+            select(Task.id, Product.serial_number)
+            .join(Product, Task.product_id == Product.id)
+            .where(Task.id.in_(task_ids))
+        )
+        for row in task_result:
+            serial_map[row[0]] = row[1]
+
+    # 组装响应
+    response_list: list[NotificationResponse] = []
+    for n in notifications:
+        resp = NotificationResponse.model_validate(n)
+        if n.task_id and n.task_id in serial_map:
+            resp.product_serial_number = serial_map[n.task_id]
+        response_list.append(resp)
+
     return NotificationListResponse(
-        notifications=[
-            NotificationResponse.model_validate(n) for n in notifications
-        ],
+        notifications=response_list,
         total=total,
         unread_count=unread_count,
     )