feat(client): 商品详情页图片支持双击全屏查看

抽出共享全屏查看器 fullscreen_image_viewer.dart（复用扫码页的
InteractiveViewer+PageView+黑底 modal），详情页缩略图双击打开，
扫码公开页改为复用同一组件去重。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/screens/products/product_detail_screen.dart

@@ -9,6 +9,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import '../../core/config/app_config.dart';
 import '../../core/utils/print_util.dart';
 import '../../widgets/label_preview_dialog.dart';
+import '../../widgets/fullscreen_image_viewer.dart';
 import '../../widgets/write_guard.dart';
 import '../../core/theme/app_theme.dart';
 import '../../models/product.dart';
@@ -309,9 +310,16 @@ class _ProductDetailScreenState extends ConsumerState<ProductDetailScreen> {
           height: 120,
           child: Row(
             children: [
-              ...p.images.map((img) => _ImageThumbnail(
-                    url: AppConfig.baseUrl + img.url,
-                    onDelete: () => _deleteImage(img),
+              ...p.images.asMap().entries.map((e) => _ImageThumbnail(
+                    url: AppConfig.baseUrl + e.value.url,
+                    onDelete: () => _deleteImage(e.value),
+                    onView: () => showFullscreenImages(
+                      context,
+                      p.images
+                          .map((img) => AppConfig.baseUrl + img.url)
+                          .toList(),
+                      initialIndex: e.key,
+                    ),
                   )),
               if (p.images.length < 5)
                 WriteGuard(
@@ -567,7 +575,9 @@ class _ProductDetailScreenState extends ConsumerState<ProductDetailScreen> {
 class _ImageThumbnail extends StatelessWidget {
   final String url;
   final VoidCallback onDelete;
-  const _ImageThumbnail({required this.url, required this.onDelete});
+  final VoidCallback onView;
+  const _ImageThumbnail(
+      {required this.url, required this.onDelete, required this.onView});
 
   @override
   Widget build(BuildContext context) {
@@ -575,19 +585,22 @@ class _ImageThumbnail extends StatelessWidget {
       padding: const EdgeInsets.only(right: 8),
       child: Stack(
         children: [
-          ClipRRect(
-            borderRadius: BorderRadius.circular(4),
-            child: Image.network(
-              url,
-              width: 110,
-              height: 110,
-              fit: BoxFit.cover,
-              errorBuilder: (_, __, ___) => Container(
+          GestureDetector(
+            onDoubleTap: onView,
+            child: ClipRRect(
+              borderRadius: BorderRadius.circular(4),
+              child: Image.network(
+                url,
                 width: 110,
                 height: 110,
-                color: AppTheme.border,
-                child: const Icon(Icons.broken_image,
-                    color: AppTheme.textSecondary),
+                fit: BoxFit.cover,
+                errorBuilder: (_, __, ___) => Container(
+                  width: 110,
+                  height: 110,
+                  color: AppTheme.border,
+                  child: const Icon(Icons.broken_image,
+                      color: AppTheme.textSecondary),
+                ),
               ),
             ),
           ),