fix(shop): 修正购物车页面跳转为切换标签页

- 将购物车按钮点击事件由 navigateTo 改为 switchTab
- 统一购物车跳转逻辑，提升用户体验
- 修复商品详情页跳转购物车方式错误问题

src/pages/shop/index.tsx

@@ -361,7 +361,7 @@ const ShopPage: React.FC = () => {
           zIndex: 999,
           boxShadow: '0 2px 8px rgba(0,0,0,0.15)',
         }}
-        onClick={() => Taro.navigateTo({ url: '/pages/shop/cart' })}
+        onClick={() => Taro.switchTab({ url: '/pages/shop/cart' })}
       >
         <Image
           className='w-7 h-7'

src/pages/shop/product-detail.tsx

@@ -199,7 +199,7 @@ const ProductDetailPage: React.FC = () => {
   }
 
   const handleGoCart = () => {
-    Taro.navigateTo({ url: '/pages/shop/cart' })
+    Taro.switchTab({ url: '/pages/shop/cart' })
   }
 
   if (!product) {