fix(client): 商品公开页暂无图片时显示门店名首字，替换硬编码岩美

_EmptyGalleryContent 接收 shopName 参数，无图片时展示
门店名第一个字符的文字头像，不再显示品牌名。

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

client/lib/screens/public/public_product_screen.dart

@@ -130,7 +130,7 @@ class _PublicProductScreenState extends State<PublicProductScreen> {
               slivers: [
                 // 1. Gallery
                 SliverToBoxAdapter(
-                  child: _HeroGallery(imageUrls: imageUrls),
+                  child: _HeroGallery(imageUrls: imageUrls, shopName: shop?['name'] as String? ?? ''),
                 ),
                 // 2. Verified ribbon
                 SliverToBoxAdapter(
@@ -227,7 +227,8 @@ class _PublicProductScreenState extends State<PublicProductScreen> {
 
 class _HeroGallery extends StatefulWidget {
   final List<String> imageUrls;
-  const _HeroGallery({required this.imageUrls});
+  final String shopName;
+  const _HeroGallery({required this.imageUrls, this.shopName = ''});
 
   @override
   State<_HeroGallery> createState() => _HeroGalleryState();
@@ -280,7 +281,7 @@ class _HeroGalleryState extends State<_HeroGallery> {
           ),
           // Image or placeholder
           if (urls.isEmpty)
-            _EmptyGalleryContent()
+            _EmptyGalleryContent(shopName: widget.shopName)
           else
             PageView.builder(
               controller: _ctrl,
@@ -291,7 +292,7 @@ class _HeroGalleryState extends State<_HeroGallery> {
                 child: Image.network(
                   urls[i],
                   fit: BoxFit.contain,
-                  errorBuilder: (_, __, ___) => _EmptyGalleryContent(),
+                  errorBuilder: (_, __, ___) => _EmptyGalleryContent(shopName: widget.shopName),
                 ),
               ),
             ),
@@ -409,8 +410,12 @@ class _HeroGalleryState extends State<_HeroGallery> {
 }
 
 class _EmptyGalleryContent extends StatelessWidget {
+  final String shopName;
+  const _EmptyGalleryContent({this.shopName = ''});
+
   @override
   Widget build(BuildContext context) {
+    final initial = shopName.isNotEmpty ? shopName.characters.first : '店';
     return Center(
       child: Column(
         mainAxisSize: MainAxisSize.min,
@@ -421,9 +426,9 @@ class _EmptyGalleryContent extends StatelessWidget {
               color: const Color(0xFF0F3057),
               borderRadius: BorderRadius.circular(12),
             ),
-            child: const Center(
-              child: Text('岩美',
-                  style: TextStyle(color: Colors.white70, fontSize: 18, fontWeight: FontWeight.w700)),
+            child: Center(
+              child: Text(initial,
+                  style: const TextStyle(color: Colors.white70, fontSize: 28, fontWeight: FontWeight.w700)),
             ),
           ),
           const SizedBox(height: 12),