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/pages/booking/index.vue

@@ -18,7 +18,7 @@
         </div>
 
         <div class="border-box border-bottom">
-          <div class="font-size-12 color-99A0AE line-height-16 pb-12 break-all">
+          <div class="text-[12px] color-99A0AE line-height-16 pb-12 break-all">
             {{ orderData.commodityDescription }}
           </div>
 
@@ -32,9 +32,9 @@
         </div>
 
         <div class="border-box flex flex-items-center flex-justify-between pt-12">
-          <span class="font-size-12 color-525866 line-height-18">取消政策及说明</span>
+          <span class="text-[12px] color-525866 line-height-18">取消政策及说明</span>
           <div class="flex flex-items-center">
-            <span class="font-size-12 theme-color-500 line-height-16" @click="refundVisible = true">取消政策</span>
+            <span class="text-[12px] theme-color-500 line-height-16" @click="refundVisible = true">取消政策</span>
             <uni-icons type="right" size="15" color="#99A0AE" />
           </div>
         </div>