feat(warning): 库存预警邮件表格增加缺少数量列（当前库存 | 缺少数量）

inventory-backend/app/services/inventory_task.py

@@ -51,20 +51,19 @@ class InventoryWarningService:
         构建纯文本物料清单表格
 
         Args:
-            rows: [{"name": ..., "spec": ..., "qty": ..., "threshold": ...}, ...]
+            rows: [{"name": ..., "spec": ..., "qty": ..., "threshold": ..., "shortfall": ...}, ...]
             level: "red" 或 "yellow"，决定阈值列标题
         """
-        threshold_label = "红色阈值" if level == "red" else "黄色阈值"
         lines = [
-            "名称 | 规格 | 当前库存 | " + threshold_label,
-            "-" * 60,
+            "名称 | 规格 | 当前库存 | 缺少数量",
+            "-" * 55,
         ]
         for r in rows:
             name = r.get('name', '-') or '-'
             spec = r.get('spec', '-') or '-'
             qty  = r.get('qty', '-')
-            th   = r.get('threshold', '-')
-            lines.append(f"{name} | {spec} | {qty} | {th}")
+            shortfall = r.get('shortfall', '-')
+            lines.append(f"{name} | {spec} | {qty} | 差{shortfall}个")
         return '\n'.join(lines)
 
     @staticmethod
@@ -141,6 +140,7 @@ class InventoryWarningService:
                         'spec': spec,
                         'qty': round(inv, 2),
                         'threshold': round(red_th, 2),
+                        'shortfall': round(red_th - inv, 2),
                     }
                     if use_yellow_channel:
                         for email in emails_to_use:
@@ -176,6 +176,7 @@ class InventoryWarningService:
                         'spec': spec,
                         'qty': round(inv, 2),
                         'threshold': round(yellow_th, 2),
+                        'shortfall': round(yellow_th - inv, 2),
                     }
                     if use_red_channel:
                         for email in emails_to_use: