feat(uniapp): 按设计稿重构首页并修复点餐分类高亮

重构米糖风格首页与纵向渐变背景；点击分类时锁定 scroll 回写，避免左侧高亮回跳到上一项。

Co-authored-by: Cursor <cursoragent@cursor.com>

yshop-drink-uniapp-vue3/pages.json

@@ -3,7 +3,9 @@
     {
       "path": "pages/index/index",
       "style": {
-        "navigationBarTitleText": "首页"
+        "navigationBarTitleText": "首页",
+        "navigationBarBackgroundColor": "#fff3e6",
+        "backgroundColor": "#fff3e6"
       }
     },