feat: 扫码商品详情页重设计 + 宣传主页 + nginx 路由完善

- public_product_screen: 1:1 复刻设计稿，新增商品介绍、批次防伪（自定义圆形印章）、完整商品参数表、门店营业时间、页脚链接
- app_theme: 完整品牌色系（brand/gray/accent/semantic）
- shop model: 新增 business_hours 字段，public 接口同步返回
- nginx: 新增 /product/ → Flutter app 扫码入口，修复 /docs /download html 后缀兼容
- web/: 新增宣传主页、功能页、文档页、扫码 HTML 及设计资源
- app_shell: 界面优化

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

client/lib/core/router/app_router.dart

@@ -37,16 +37,17 @@ class _RouterNotifier extends ChangeNotifier {
   String? redirect(BuildContext context, GoRouterState state) {
     final authState = _ref.read(authStateProvider);
     final isLoggedIn = authState.isLoggedIn;
-    final isLoginRoute = state.matchedLocation == '/login';
-    final isPublicRoute = state.matchedLocation.startsWith('/product/');
+    final loc = state.matchedLocation;
+    final isPublicRoute = loc == '/login' ||
+        loc.startsWith('/product/');
     final result = !authState.initialized
         ? null
-        : (!isLoggedIn && !isLoginRoute && !isPublicRoute)
+        : (!isLoggedIn && !isPublicRoute)
             ? '/login'
-            : (isLoggedIn && isLoginRoute)
+            : (isLoggedIn && loc == '/login')
                 ? '/stock-in'
                 : null;
-    debugPrint('[Router] redirect: location=${state.matchedLocation}'
+    debugPrint('[Router] redirect: location=$loc'
         ' initialized=${authState.initialized}'
         ' isLoggedIn=$isLoggedIn'
         ' → ${result ?? "null (no redirect)"}');
@@ -71,7 +72,7 @@ final appRouterProvider = Provider<GoRouter>((ref) {
     refreshListenable: notifier,
     redirect: notifier.redirect,
     routes: [
-      // Public route — no auth, no shell nav bar
+      // Public product scan — no auth, no shell nav bar
       GoRoute(
         path: '/product/:public_id',
         builder: (context, state) =>