feat: 任务详情页语音播报功能 (REQ-20260508-0006)

- 详情页右侧悬浮播放按钮（36dp半透明圆形）
- 播报内容：任务名+地点+时间+积分(>0)+备注，空字段跳过
- 播放中按钮高亮+图标切换，再点停止
- 离开页面自动停止播放
- TTS播放期间抑制提示音，避免叠加

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

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

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- 喇叭图标（语音播报按钮）24×24dp -->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <!-- 喇叭主体 -->
+    <path
+        android:fillColor="@color/text_primary"
+        android:pathData="M3,9v6h4l5,5V4L7,9H3z" />
+    <!-- 声波 -->
+    <path
+        android:fillColor="@color/text_primary"
+        android:pathData="M16.5,12c0,-1.77 -1.02,-3.29 -2.5,-4.03v8.05c1.48,-0.73 2.5,-2.25 2.5,-4.02z" />
+    <path
+        android:fillColor="@color/text_primary"
+        android:pathData="M14,3.23v2.06c2.89,0.86 5,3.54 5,6.71s-2.11,5.85 -5,6.71v2.06c4.01,-0.91 7,-4.49 7,-8.77s-2.99,-7.86 -7,-8.77z" />
+</vector>