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/finance/finance_screen.dart

@@ -7,6 +7,7 @@ import '../../widgets/data_table_card.dart';
 import '../../widgets/multi_select_dropdown.dart' show ColDef, ColumnToggleButton, FilterableColumnHeader;
 import '../../widgets/page_scaffold.dart';
 import '../../providers/connectivity_provider.dart';
+import '../../core/utils/export_util.dart';
 
 class FinanceScreen extends ConsumerWidget {
   const FinanceScreen({super.key});
@@ -41,10 +42,12 @@ class _FinanceTab extends ConsumerStatefulWidget {
 class _FinanceTabState extends ConsumerState<_FinanceTab> {
   late String _month;
   int _page = 1;
+  int _pageSize = 20;
 
   // We drive fetches by maintaining a Future locally, bypassing the global provider
   late Future<List<FinanceRecord>> _future;
   List<FinanceRecord> _allRecords = [];
+  int _total = 0;
 
   Set<String> _filterType = {};
   Set<String> _filterPartner = {};
@@ -75,10 +78,11 @@ class _FinanceTabState extends ConsumerState<_FinanceTab> {
           type: widget.typeFilter.isEmpty ? null : widget.typeFilter,
           month: _month,
           page: _page,
-          pageSize: 50,
+          pageSize: _pageSize,
         )
         .then((r) {
       _allRecords = r.data;
+      _total = r.total;
       return r.data;
     });
   }
@@ -294,16 +298,50 @@ class _FinanceTabState extends ConsumerState<_FinanceTab> {
           const Divider(height: 1),
         Expanded(
           child: DataTableCard(
-            totalCount: records.length,
+            totalCount: _total > 0 ? _total : records.length,
             page: _page,
+            pageSize: _pageSize,
             onPageChanged: (p) {
               setState(() {
                 _page = p;
                 _fetch();
               });
             },
+            onPageSizeChanged: (s) {
+              setState(() {
+                _pageSize = s;
+                _page = 1;
+                _fetch();
+              });
+            },
             toolbar: Row(
               children: [
+                OutlinedButton.icon(
+                  onPressed: () {
+                    final tabName = widget.typeFilter.isEmpty
+                        ? '财务全部记录'
+                        : widget.typeFilter == 'payable'
+                            ? '应付账款'
+                            : '应收账款';
+                    exportExcel(
+                      filename: tabName,
+                      headers: ['日期', '类型', '往来单位', '关联单据', '金额', '余额', '备注'],
+                      rows: records.map((r) => [
+                        r.recordDate?.substring(0, 10) ?? '',
+                        r.typeLabel,
+                        r.partnerName ?? '',
+                        r.refType != null && r.refId != null
+                            ? '${r.refType!.replaceAll('_', '-')}#${r.refId}'
+                            : '',
+                        r.amount,
+                        r.balance,
+                        r.remark ?? '',
+                      ]).toList(),
+                    );
+                  },
+                  icon: const Icon(Icons.download, size: 16),
+                  label: const Text('导出'),
+                ),
                 const Spacer(),
                 _MonthSelector(
                   value: _month,