refactor: replace border-box with box-border and clean up unused scss

Remove the unused box-sizing.scss stylesheet and its import from the main SCSS index file.
Update all Vue component template class references from the custom border-box class to the
native box-border utility class to eliminate redundant custom CSS and align with the project's
utility class conventions.

src/components/SwipeCards/index.vue

@@ -1,5 +1,5 @@
 <template>
-  <view class="card border-box pb-[12px] relative mt-12">
+  <view class="card box-border pb-[12px] relative mt-12">
     <view class="card-item absolute overflow-hidden" v-for="(card, index) in list" :key="card.__uid"
       :style="[itemStyle(index, card), transformStyle(index, card)]" @touchstart.stop="touchStart($event, index)"
       @touchmove.stop.prevent="touchMove($event, index)" @touchend.stop="touchEnd(index)"
@@ -11,7 +11,7 @@
         </view>
 
         <!-- 底部：价格 + 购买按钮 -->
-        <view class="card-footer border-box p-[12px] flex flex-justify-between flex-items-center">
+        <view class="card-footer box-border p-[12px] flex flex-justify-between flex-items-center">
           <view class="border-box">
             <view class="font-size-14 font-500 color-333 ellipsis-1">
               {{ card.commodityName }}