style: migrate font-size classes to text-[size] syntax

Additionally update spacing utilities and refactor the OrderQrcode component:
- Switch popup implementation from uni-popup to van-popup
- Remove the deprecated SCSS stylesheet
- Clean up component template and script code

src/components/RefundPopup/index.vue

@@ -14,11 +14,11 @@
           <uni-icons fontFamily="znicons" size="20" color="#333">
             {{ iconsMap["zn-refund"] }}
           </uni-icons>
-          <span class="font-size-14 font-600 color-171717 ml-8">
+          <span class="text-[14px] font-600 color-171717 ml-8">
             {{ refundTitle }}
           </span>
         </div>
-        <div class="font-size-14 color-525866 line-height-16 mb-4" v-for="(item, index) in commodityPurchaseInstruction"
+        <div class="text-[14px] color-525866 line-height-16 mb-4" v-for="(item, index) in commodityPurchaseInstruction"
           :key="index">
           {{ item }}
         </div>