feat: 完成7项功能任务

后端：
- fix(backend): InventoryLog 增加 Product/Warehouse 关联，Logs 接口加 Preload 修复流水记录显示"-"
- feat(backend): 新增 /inventory/batches 批次追踪接口
- feat(backend): 新增财务记录、编号规则接口（finance、number_rule handler）
- fix(backend): service/stock_test.go 修复 model.Date 类型错误

前端：
- feat(client): 入库/出库管理 Tab 调换顺序（审核在前），审核 Tab 加新建按钮，列表 Tab 无按钮
- feat(client): 入库单/出库单增加详情弹窗，显示完整单据信息和商品明细
- feat(client): 完善出库单新建表单（StockOutFormScreen），支持选客户/仓库/商品
- fix(client): StockInItem/StockOutItem.fromJson 修复读取嵌套 product 对象而非平铺字段
- feat(client): 批次追踪页面（BatchTrackingScreen）及侧边栏入口
- feat(client): 财务管理、盘点、编号规则接入真实后端 API
- fix(client): 入库/出库审核通过后 invalidate inventoryListProvider 刷新库存

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/models/stock_out.dart

@@ -29,10 +29,10 @@ class StockOutItem {
         quantity: (json['quantity'] as num).toDouble(),
         unitPrice: (json['unit_price'] as num).toDouble(),
         totalPrice: (json['total_price'] as num).toDouble(),
-        productName: json['product_name'] as String?,
-        productCode: json['product_code'] as String?,
-        productSpec: json['product_spec'] as String?,
-        productUnit: json['product_unit'] as String?,
+        productName: (json['product'] as Map<String, dynamic>?)?['name'] as String?,
+        productCode: (json['product'] as Map<String, dynamic>?)?['code'] as String?,
+        productSpec: (json['product'] as Map<String, dynamic>?)?['spec'] as String?,
+        productUnit: (json['product'] as Map<String, dynamic>?)?['unit'] as String?,
       );
 }