feat(client): 出库明细成本/售价/利润三列重设计 + 建单利润列 + 入库列头统一

- 出库详情抽屉（管理员）：数量/成本价/售价/利润 + 合计金额/合计利润 双行；
  operator 见 售价/小计（服务端抹零+前端隐藏双保险）；利润负数 danger
- 出库建单：商品名称下带编码（字体同系列列）；金额列→利润列（实时）；
  底栏合计利润（仅管理员）；进价列仅管理员；提交发新 key（cost_price/sale_price）
- 入库建单列头：进价（单瓶）/ 参考售价 / 总进价
- 退单弹窗金额改售价口径（与冲应收一致）；打印保留待定价回退成本兼容
- models 字段随后端消歧改名；golden 重打；新增抽屉双形态 widget 测试

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JJ1g8XV1YhhmHRzhwWEW7o

client/lib/models/stock_in.dart

@@ -3,8 +3,8 @@ class StockInItem {
   final int? orderId;
   final int productId;
   final double quantity;
-  final double unitPrice;
-  final double totalPrice;
+  final double costPrice; // 进价（单瓶）
+  final double costAmount; // 总进价 = quantity × costPrice
   final double returnedQuantity; // 0=未退；>=quantity 表示整行已退单
   final String? batchNo;
   final String? productionDate;
@@ -26,8 +26,8 @@ class StockInItem {
     this.orderId,
     required this.productId,
     required this.quantity,
-    required this.unitPrice,
-    required this.totalPrice,
+    required this.costPrice,
+    required this.costAmount,
     this.returnedQuantity = 0,
     this.batchNo,
     this.productionDate,
@@ -57,8 +57,8 @@ class StockInItem {
           json['order_id'] != null ? (json['order_id'] as num).toInt() : null,
       productId: (json['product_id'] as num).toInt(),
       quantity: (json['quantity'] as num).toDouble(),
-      unitPrice: (json['unit_price'] as num).toDouble(),
-      totalPrice: (json['total_price'] as num).toDouble(),
+      costPrice: (json['cost_price'] as num?)?.toDouble() ?? 0,
+      costAmount: (json['cost_amount'] as num?)?.toDouble() ?? 0,
       returnedQuantity: (json['returned_quantity'] as num?)?.toDouble() ?? 0,
       batchNo: json['batch_no'] as String?,
       productionDate: json['production_date'] as String?,
@@ -81,8 +81,8 @@ class StockInItem {
   Map<String, dynamic> toJson() => {
         'product_id': productId,
         'quantity': quantity,
-        'unit_price': unitPrice,
-        'total_price': totalPrice,
+        'cost_price': costPrice,
+        'cost_amount': costAmount,
         if (batchNo != null) 'batch_no': batchNo,
         if (productionDate != null) 'production_date': productionDate,
       };
@@ -104,7 +104,7 @@ class StockInOrder {
   final String returnState; // none | partial | full（退单状态）
   final String? orderDate;
   final String? reviewedAt;
-  final double? totalAmount;
+  final double? costTotal; // 应付合计 = Σ 总进价
   final String? remark;
   final List<StockInItem> items;
 
@@ -124,7 +124,7 @@ class StockInOrder {
     this.returnState = 'none',
     this.orderDate,
     this.reviewedAt,
-    this.totalAmount,
+    this.costTotal,
     this.remark,
     this.items = const [],
   });
@@ -155,8 +155,8 @@ class StockInOrder {
         returnState: json['return_state'] as String? ?? 'none',
         orderDate: json['order_date'] as String?,
         reviewedAt: json['reviewed_at'] as String?,
-        totalAmount: json['total_amount'] != null
-            ? (json['total_amount'] as num).toDouble()
+        costTotal: json['cost_total'] != null
+            ? (json['cost_total'] as num).toDouble()
             : null,
         remark: json['remark'] as String?,
         items: json['items'] != null