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/home/components/ChatTopWelcome/index.vue

@@ -6,7 +6,7 @@ v
         <SpriteAnimator :src="spriteStyle.ipLargeImage" :frameWidth="spriteStyle.frameWidth"
           :frameHeight="spriteStyle.frameHeight" :totalFrames="spriteStyle.totalFrames" :columns="spriteStyle.columns"
           :displayWidth="spriteStyle.displayWidth" :fps="16" />
-        <div class="welcome-text font-size-14 font-500 font-family-misans-vf color-171717 line-height-24">
+        <div class="welcome-text text-[14px] font-500 font-family-misans-vf color-171717 line-height-24">
           {{ welcomeContent }}
         </div>
       </div>