fix: 留言板区分业务序列号与系统追溯码

语义修正:
  Product.serial_number  = 16位HEX系统追溯码(如000000000000000D)
  Product.external_serial = 业务产品序列号(如25022)

后端:
  - ProductMessageItem 新增 external_serial 字段
  - search_product_messages 关联查询 Product.external_serial
  - 关键词搜索也支持按 external_serial 匹配

前端显示:
  样品升降台V1J · 序列号: 25022          ← 醒目
  追溯码: 000000000000000D               ← 10px浅灰小字

backend/app/services/dashboard_service.py

@@ -37,10 +37,11 @@ class WipTask(BaseModel):
 class ProductMessageItem(BaseModel):
     id: str
     content: str
-    operator_name: str         # 留言人中文姓名
-    product_sn: str            # 16位SN
-    material_name: str         # 物料名称
-    created_at: str            # ISO时间字符串
+    operator_name: str            # 留言人中文姓名
+    product_sn: str               # 16位HEX系统追溯码
+    external_serial: str | None   # 业务产品序列号（如 25022）
+    material_name: str            # 物料名称
+    created_at: str               # ISO时间字符串
 
 
 class ProductMessageList(BaseModel):
@@ -194,9 +195,9 @@ async def search_product_messages(
     from app.models.product import Product
     from app.core.time_utils import BEIJING_TZ
 
-    # 基础查询
+    # 基础查询 — 同时取出 16位追溯码 + 业务序列号
     stmt = (
-        select(ProductMessage, Product.serial_number, Product.material_name)
+        select(ProductMessage, Product.serial_number, Product.material_name, Product.external_serial)
         .join(Product, ProductMessage.product_id == Product.id)
     )
 
@@ -205,6 +206,7 @@ async def search_product_messages(
         kw = f"%{keyword.strip()}%"
         stmt = stmt.where(or_(
             Product.serial_number.ilike(kw),
+            Product.external_serial.ilike(kw),
             Product.material_name.ilike(kw),
             ProductMessage.operator_id.ilike(kw),
             ProductMessage.content.ilike(kw),
@@ -227,7 +229,7 @@ async def search_product_messages(
         name_map = get_display_names(raw_ids)
 
     items: list[ProductMessageItem] = []
-    for msg, sn, mat_name in rows:
+    for msg, sn, mat_name, ext_sn in rows:
         t = msg.created_at
         if t:
             if t.tzinfo is None:
@@ -243,6 +245,7 @@ async def search_product_messages(
             content=msg.content,
             operator_name=name_map.get(msg.operator_id, msg.operator_id),
             product_sn=sn or "",
+            external_serial=ext_sn or None,
             material_name=mat_name or "",
             created_at=time_str,
         ))