feat: add scroll top mask, unify page top spacing and docs

src/pages/shop/detail/index.tsx

@@ -8,6 +8,7 @@ import { useSafeArea } from '../../../hooks/useSafeArea'
 import { useStatusBar } from '../../../hooks/useStatusBar'
 import { useThemeContext } from '../../../context/ThemeContext'
 import ThemedPageMeta from '../../../components/ThemedPageMeta'
+import ScrollTopMask from '../../../components/ScrollTopMask'
 import BottomActionBar from '../../../components/BottomActionBar'
 
 const clamp = (v: number, min: number, max: number) => Math.min(Math.max(v, min), max)
@@ -111,6 +112,7 @@ export default function ShopDetailPage() {
     return (
       <View className="shop-detail-page theme-dark">
         <ThemedPageMeta darkTop />
+      <ScrollTopMask title="商品详情" targetSelector=".shop-back-btn" showBack />
         <Text style={{ color: '#fff', padding: '40rpx' }}>商品不存在</Text>
       </View>
     )
@@ -119,6 +121,7 @@ export default function ShopDetailPage() {
   return (
     <View className="shop-detail-page theme-dark">
       <ThemedPageMeta darkTop />
+      <ScrollTopMask title="商品详情" targetSelector=".shop-back-btn" showBack />
       {/* Fixed Hero */}
       <View className="shop-hero-fixed">
         <View