批次5：inventory服务下沉收口 + Pydantic v2 / datetime弃用清零

- inventory业务层下沉（薄路由+service orchestration模式）：
  - customer/supplier/warehouse -> master_data_service
  - material_routes（价格历史/趋势/供应商关联）-> material_service
  - product_routes（CRUD/BOM/from-task跨模块桥接）-> product_service
  - dashboard_routes（首页统计/低库存预警）-> dashboard_service
- inventory侧新增service回归覆盖（dashboard 2 / master_data 10 /
  material 10 / product 14），含跨模块桥接测试种子
- Pydantic v2弃用清零：全仓14处 class Config 全部迁移到
  model_config = ConfigDict(from_attributes=True)（含 shared auth）
- datetime.utcnow() 弃用清零：auth_service 3处统一改 datetime.now(timezone.utc)
- 同步文档：STATUS / ROADMAP / TECH_DEBT（D12清偿）/ AGENTS 代码地图

测试基线：126 passed, 4 skipped（无deprecation warning）

Co-Authored-By: Claude Code <noreply@anthropic.com>

src/inventory/services/dashboard_service.py

@@ -0,0 +1,71 @@
+"""仪表盘聚合业务服务层
+
+将 dashboard_routes 中的聚合查询与统计编排下沉到此，
+路由层只做依赖注入与响应返回。
+"""
+from sqlalchemy import func, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from inventory.models import Customer, Inventory, Product, PurchaseOrder, SalesOrder, Supplier, Warehouse
+
+
+class DashboardService:
+    """仪表盘统计服务"""
+
+    @staticmethod
+    async def get_dashboard(db_session: AsyncSession) -> dict:
+        material_count = await db_session.scalar(
+            select(func.count(Product.id)).where(Product.is_active == True, Product.item_type == "material")
+        ) or 0
+        finished_product_count = await db_session.scalar(
+            select(func.count(Product.id)).where(Product.is_active == True, Product.item_type == "finished")
+        ) or 0
+        supplier_count = await db_session.scalar(select(func.count(Supplier.id)).where(Supplier.is_active == True)) or 0
+        customer_count = await db_session.scalar(select(func.count(Customer.id)).where(Customer.is_active == True)) or 0
+        warehouse_count = await db_session.scalar(select(func.count(Warehouse.id)).where(Warehouse.is_active == True)) or 0
+
+        total_stock = await db_session.scalar(
+            select(func.sum(Inventory.quantity))
+            .join(Product, Inventory.product_id == Product.id)
+            .where(Product.item_type == "material")
+        ) or 0
+        total_value = await db_session.scalar(
+            select(func.sum(Inventory.quantity * Product.cost_price))
+            .join(Product, Inventory.product_id == Product.id)
+            .where(Product.item_type == "material")
+        ) or 0
+
+        pending_purchase = await db_session.scalar(
+            select(func.count(PurchaseOrder.id)).where(PurchaseOrder.status == "pending")
+        ) or 0
+        pending_sales = await db_session.scalar(
+            select(func.count(SalesOrder.id)).where(SalesOrder.status == "pending")
+        ) or 0
+
+        low_stock_products = await db_session.execute(
+            select(Product, Inventory)
+            .join(Inventory, Product.id == Inventory.product_id)
+            .where(Product.item_type == "material")
+            .where(Inventory.quantity <= Product.min_stock)
+            .limit(10)
+        )
+        low_stock = [
+            {"id": p.id, "name": p.name, "sku": p.sku, "quantity": i.quantity, "min_stock": p.min_stock}
+            for p, i in low_stock_products.all()
+        ]
+
+        return {
+            "finished_product_count": finished_product_count,
+            "material_count": material_count,
+            "supplier_count": supplier_count,
+            "customer_count": customer_count,
+            "warehouse_count": warehouse_count,
+            "total_stock": total_stock,
+            "total_value": round(total_value, 2),
+            "pending_purchase": pending_purchase,
+            "pending_sales": pending_sales,
+            "low_stock_products": low_stock,
+        }
+
+
+dashboard_service = DashboardService()