feat: 商品详情页、XLS导入修复、分页选择器、导出功能

后端：
- 新增 product_images 表，支持每商品最多5张图（服务端压缩至1200px/JPEG85%）
- products 表新增 public_id(UUID)、description 字段
- 新增商品详情接口、二维码接口、公开商品接口（无鉴权）
- 修复 XLS 导入：OLE2 magic bytes 检测 + 临时文件解析，兼容 extrame/xls
- 修复商品/名称/系列/规格三张表导入数据为0（LastCol()=0 bug）
- 所有导入接口返回 total/imported/skipped 统计
- config 新增 StorageConfig，支持 STORAGE_* 环境变量覆盖
- 种子数据修复：products 补 public_id、新增 product_images TRUNCATE、schema.sql 表名修正

前端：
- 商品详情页：图片上传/删除、描述内联编辑、二维码弹窗、公开链接复制
- 公开商品页：无鉴权路由 /product/:public_id，Flutter Web SPA
- 商品详情列表（批次追踪）商品名超链接跳转详情页
- 导航「商品管理」改名「商品详情」
- 所有列表表格新增每页条数选择（10/20/50/100）
- 表格列头内嵌筛选（FilterableColumnHeader）
- 导出 Excel 功能（入库/出库/库存/财务/批次/往来单位）
- 网络恢复自动刷新 + 离线缓存展示

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

client/lib/models/stock_out.dart

@@ -6,6 +6,7 @@ class StockOutItem {
   final double totalPrice;
   final String? productName;
   final String? productCode;
+  final String? productSeries;
   final String? productSpec;
   final String? productUnit;
 
@@ -17,6 +18,7 @@ class StockOutItem {
     required this.totalPrice,
     this.productName,
     this.productCode,
+    this.productSeries,
     this.productSpec,
     this.productUnit,
   });
@@ -31,6 +33,7 @@ class StockOutItem {
         totalPrice: (json['total_price'] as num).toDouble(),
         productName: (json['product'] as Map<String, dynamic>?)?['name'] as String?,
         productCode: (json['product'] as Map<String, dynamic>?)?['code'] as String?,
+        productSeries: (json['product'] as Map<String, dynamic>?)?['series'] as String?,
         productSpec: (json['product'] as Map<String, dynamic>?)?['spec'] as String?,
         productUnit: (json['product'] as Map<String, dynamic>?)?['unit'] as String?,
       );
@@ -45,6 +48,9 @@ class StockOutOrder {
   final int? partnerId;
   final String? partnerName;
   final int? operatorId;
+  final String? operatorName;
+  final int? reviewerId;
+  final String? reviewerName;
   final String status; // draft | pending | approved | rejected
   final String? orderDate;
   final double? totalAmount;
@@ -60,6 +66,9 @@ class StockOutOrder {
     this.partnerId,
     this.partnerName,
     this.operatorId,
+    this.operatorName,
+    this.reviewerId,
+    this.reviewerName,
     required this.status,
     this.orderDate,
     this.totalAmount,
@@ -80,6 +89,11 @@ class StockOutOrder {
         operatorId: json['operator_id'] != null
             ? (json['operator_id'] as num).toInt()
             : null,
+        operatorName: (json['operator'] as Map<String, dynamic>?)?['real_name'] as String?,
+        reviewerId: json['reviewer_id'] != null
+            ? (json['reviewer_id'] as num).toInt()
+            : null,
+        reviewerName: (json['reviewer'] as Map<String, dynamic>?)?['real_name'] as String?,
         status: json['status'] as String,
         orderDate: json['order_date'] as String?,
         totalAmount: json['total_amount'] != null