fix(mobile): precise centering in ask page switch and composer

Replace line-height centering with flex + fixed heights, and swap
emoji/unicode glyphs (＋ × ⌨ 🎤) for uni-icons vector icons so
alignment and rendering are consistent across platforms.

mobile-uni/src/pages/user/sop/index.vue

@@ -2013,15 +2013,20 @@ onUnload(() => {
 }
 
 .chat-source-switch .source-option {
+  display: flex;
   flex: 1;
+  align-items: center;
+  justify-content: center;
+  box-sizing: border-box;
+  height: 32px;
   margin: 0;
-  padding: 6px 0;
+  padding: 0;
   border: none;
   border-radius: 999px;
   background: transparent;
   color: #5a6270;
   font-size: 14px;
-  line-height: 1.3;
+  line-height: 1.2;
 }
 
 .chat-source-switch .source-option.active {
@@ -2403,7 +2408,7 @@ onUnload(() => {
 }
 
 .chat-source-switch .source-option {
-  padding: 5px 0;
+  height: 30px;
   font-size: 13px;
 }