fix(mobile): replace emoji glyphs with uni-icons and flex centering app-wide

- ChatComposer panel contract: callers now pass uni-icons type names
  (image/sound/list/help/checkmark) instead of emoji
- voice playback buttons: sound icon + pulse animation, no more 🔊/◼ chars
- practice recent list: rare symbols ⌕⌁◉ (tofu risk) -> wallet/gear/chatbubble
- sop resource icon ▶/文 -> 视/文 character badges
- back arrows: 22 char-based ← -> uni-icons back across 21 pages
- line-height centering -> flex in 8 spots (back buttons, media-remove,
  turn-voice capsule, option-marker, text-button, play-question)

mobile-uni/src/pages/candidate/interview/index.vue

@@ -1,7 +1,7 @@
 <template>
   <view class="page candidate-subpage interview-page">
     <view class="subpage-header">
-      <button class="subpage-back-button" aria-label="返回候选首页" title="返回候选首页" @click="goBack">←</button>
+      <button class="subpage-back-button" aria-label="返回候选首页" title="返回候选首页" @click="goBack"><uni-icons type="back" size="20" color="#25282d" /></button>
       <view class="subpage-heading">
         <text class="page-title">面试任务</text>
         <text class="page-subtitle">生活顾问结构化面试</text>