refactor: replace legacy flex utility classes and remove flex.scss

Replace all instances of prefixed flex utility classes (like flex-items-center, flex-justify-between, flex-full, flex-shrink-0) with their standard un-prefixed counterparts (items-center, justify-between, flex-1, shrink-0) across the codebase. Remove the deprecated src/static/scss/flex.scss partial file as it is no longer needed after these updates.

src/components/SwipeCards/index.vue

@@ -11,7 +11,7 @@
         </view>
 
         <!-- 底部：价格 + 购买按钮 -->
-        <view class="card-footer p-[12px] flex flex-justify-between flex-items-center">
+        <view class="card-footer p-[12px] flex justify-between items-center">
           <view class="border-box">
             <view class="text-[14px] font-[500] text-[#333333] truncate">
               {{ card.commodityName }}