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/screens/partners/partners_screen.dart

@@ -7,6 +7,7 @@ import '../../models/partner.dart';
 import '../../providers/partner_provider.dart';
 import '../../widgets/data_table_card.dart';
 import '../../widgets/page_scaffold.dart';
+import '../../core/utils/export_util.dart';
 
 class PartnersScreen extends ConsumerStatefulWidget {
   const PartnersScreen({super.key});
@@ -78,6 +79,8 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
         },
         onPageChanged: (p) =>
             ref.read(supplierListProvider.notifier).setPage(p),
+        onPageSizeChanged: (s) =>
+            ref.read(supplierListProvider.notifier).setPageSize(s),
         onAdd: () => _showPartnerDialog(context, isSupplier: true),
         onEdit: (p) =>
             _showPartnerDialog(context, isSupplier: true, partner: p),
@@ -119,6 +122,8 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
         },
         onPageChanged: (p) =>
             ref.read(customerListProvider.notifier).setPage(p),
+        onPageSizeChanged: (s) =>
+            ref.read(customerListProvider.notifier).setPageSize(s),
         onAdd: () => _showPartnerDialog(context, isSupplier: false),
         onEdit: (p) =>
             _showPartnerDialog(context, isSupplier: false, partner: p),
@@ -133,6 +138,7 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
     required TextEditingController searchCtrl,
     required void Function(String) onSearchChanged,
     required void Function(int) onPageChanged,
+    required void Function(int) onPageSizeChanged,
     required VoidCallback onAdd,
     required void Function(Partner) onEdit,
     required void Function(Partner) onDelete,
@@ -141,7 +147,9 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
     return DataTableCard(
       totalCount: result.total,
       page: result.page,
+      pageSize: result.pageSize,
       onPageChanged: onPageChanged,
+      onPageSizeChanged: onPageSizeChanged,
       toolbar: Row(
         children: [
           ElevatedButton.icon(
@@ -149,6 +157,19 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
             icon: const Icon(Icons.add, size: 16),
             label: Text(isSupplier ? '新建' : '新建'),
           ),
+          const SizedBox(width: 8),
+          OutlinedButton.icon(
+            onPressed: () => exportExcel(
+              filename: isSupplier ? '供应商列表' : '客户列表',
+              headers: ['编码', '名称', '联系人', '电话', '地址', '备注'],
+              rows: partners.map((p) => [
+                p.code ?? '', p.name, p.contact ?? '',
+                p.phone ?? '', p.address ?? '', p.remark ?? '',
+              ]).toList(),
+            ),
+            icon: const Icon(Icons.download, size: 16),
+            label: const Text('导出'),
+          ),
           const Spacer(),
           SizedBox(
             width: 200,
@@ -170,6 +191,7 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
         const DataColumn(label: Text('联系人')),
         const DataColumn(label: Text('联系电话')),
         const DataColumn(label: Text('地址')),
+        const DataColumn(label: Text('状态')),
         const DataColumn(label: Text('操作')),
       ],
       rows: partners.isEmpty
@@ -183,6 +205,7 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
                 const DataCell(SizedBox()),
                 const DataCell(SizedBox()),
                 const DataCell(SizedBox()),
+                const DataCell(SizedBox()),
               ])
             ]
           : partners
@@ -207,6 +230,15 @@ class _PartnersScreenState extends ConsumerState<PartnersScreen> {
                         child: Text(p.address ?? '-',
                             overflow: TextOverflow.ellipsis),
                       )),
+                      DataCell(Text(
+                        p.status == 'enabled' ? '正常' : '禁用',
+                        style: TextStyle(
+                          fontSize: 13,
+                          color: p.status == 'enabled'
+                              ? AppTheme.success
+                              : AppTheme.textSecondary,
+                        ),
+                      )),
                       DataCell(Row(
                         mainAxisSize: MainAxisSize.min,
                         children: [