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/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -5,11 +5,13 @@
 import FlutterMacOS
 import Foundation
 
+import file_picker
 import package_info_plus
 import shared_preferences_foundation
 import url_launcher_macos
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  FilePickerPlugin.register(with: registry.registrar(forPlugin: "FilePickerPlugin"))
   FPPPackageInfoPlusPlugin.register(with: registry.registrar(forPlugin: "FPPPackageInfoPlusPlugin"))
   SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))
   UrlLauncherPlugin.register(with: registry.registrar(forPlugin: "UrlLauncherPlugin"))

client/macos/Podfile.lock

@@ -1,4 +1,6 @@
 PODS:
+  - file_picker (0.0.1):
+    - FlutterMacOS
   - FlutterMacOS (1.0.0)
   - package_info_plus (0.0.1):
     - FlutterMacOS
@@ -9,12 +11,15 @@ PODS:
     - FlutterMacOS
 
 DEPENDENCIES:
+  - file_picker (from `Flutter/ephemeral/.symlinks/plugins/file_picker/macos`)
   - FlutterMacOS (from `Flutter/ephemeral`)
   - package_info_plus (from `Flutter/ephemeral/.symlinks/plugins/package_info_plus/macos`)
   - shared_preferences_foundation (from `Flutter/ephemeral/.symlinks/plugins/shared_preferences_foundation/darwin`)
   - url_launcher_macos (from `Flutter/ephemeral/.symlinks/plugins/url_launcher_macos/macos`)
 
 EXTERNAL SOURCES:
+  file_picker:
+    :path: Flutter/ephemeral/.symlinks/plugins/file_picker/macos
   FlutterMacOS:
     :path: Flutter/ephemeral
   package_info_plus:
@@ -25,6 +30,7 @@ EXTERNAL SOURCES:
     :path: Flutter/ephemeral/.symlinks/plugins/url_launcher_macos/macos
 
 SPEC CHECKSUMS:
+  file_picker: 7584aae6fa07a041af2b36a2655122d42f578c1a
   FlutterMacOS: d0db08ddef1a9af05a5ec4b724367152bb0500b1
   package_info_plus: f0052d280d17aa382b932f399edf32507174e870
   shared_preferences_foundation: 7036424c3d8ec98dfe75ff1667cb0cd531ec82bb

client/macos/Runner/DebugProfile.entitlements

@@ -10,5 +10,9 @@
 	<true/>
 	<key>com.apple.security.network.server</key>
 	<true/>
+	<key>com.apple.security.files.downloads.read-write</key>
+	<true/>
+	<key>com.apple.security.files.user-selected.read-only</key>
+	<true/>
 </dict>
 </plist>

client/macos/Runner/Release.entitlements

@@ -6,5 +6,9 @@
 	<true/>
 	<key>com.apple.security.network.client</key>
 	<true/>
+	<key>com.apple.security.files.downloads.read-write</key>
+	<true/>
+	<key>com.apple.security.files.user-selected.read-only</key>
+	<true/>
 </dict>
 </plist>