fix: 语音按钮圆角改用 radius 兼容 API 27+

topStartRadius 等属性需要 API 31，改为统一 radius=24dp

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src/main/res/drawable/bg_btn_voice.xml

@@ -1,24 +1,16 @@
 <?xml version="1.0" encoding="utf-8"?>
-<!-- 语音播放按钮：橙色药丸形（左方右圆，和旧版一致） -->
+<!-- 语音播放按钮：橙色圆角（兼容 API 27+） -->
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
     <item android:state_pressed="true">
         <shape android:shape="rectangle">
             <solid android:color="#FFCC8820" />
-            <corners
-                android:topStartRadius="8dp"
-                android:bottomStartRadius="8dp"
-                android:topEndRadius="24dp"
-                android:bottomEndRadius="24dp" />
+            <corners android:radius="24dp" />
         </shape>
     </item>
     <item>
         <shape android:shape="rectangle">
             <solid android:color="#FFEB9A26" />
-            <corners
-                android:topStartRadius="8dp"
-                android:bottomStartRadius="8dp"
-                android:topEndRadius="24dp"
-                android:bottomEndRadius="24dp" />
+            <corners android:radius="24dp" />
         </shape>
     </item>
 </selector>