feat(timer): 训练到目标时长不再自动结束,支持超长发挥

- Timer: 到时间触发 onGoalReached(提示)而非自动结束,elapsed/overtime
  继续累加直到用户手动停止
- timer: onGoalReached 播 goal 语音 + goalReached 状态;finishTraining
  补 complete 语音;完成弹窗显示"超长发挥 +X 秒"
- wxml: 超时 badge 训练中也显示;新增 goalReached hint 分支
- voice/tts: 新增 goal 语音 prompt(需部署 tts 云函数)
- config: 版本号 v2.5 -> v2.6

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pages/timer/timer.wxml

@@ -46,7 +46,7 @@
       <view class="spark s6">💪</view>
     </view>
 
-    <view class="overtime-badge" wx:if="{{isCompleted && overtime > 0}}">
+    <view class="overtime-badge" wx:if="{{overtime > 0}}">
       <image class="overtime-icon" src="{{icons.hotFill}}" mode="aspectFit"></image>
       <text>+{{overtime}}s</text>
     </view>
@@ -61,6 +61,10 @@
         <block wx:else>今日目标 {{duration}} 秒 · 第 {{planDay}} 天</block>
       </text>
     </view>
+    <view class="hint-row" wx:elif="{{status === 'running' && goalReached}}">
+      <image class="hint-icon running-pulse" src="{{icons.hotFill}}" mode="aspectFit"></image>
+      <text class="hint-text running">目标达成，继续挑战!</text>
+    </view>
     <view class="hint-row" wx:elif="{{status === 'running'}}">
       <image class="hint-icon running-pulse" src="{{icons.likeFill}}" mode="aspectFit"></image>
       <text class="hint-text running">保持姿势，核心收紧!</text>
@@ -145,7 +149,7 @@
 
       <view class="completion-overtime" wx:if="{{completionOvertime > 0}}">
         <text class="overtime-plus">+{{completionOvertime}}</text>
-        <text class="overtime-label">秒超时</text>
+        <text class="overtime-label">秒超长发挥</text>
       </view>
 
       <view class="completion-streak" wx:if="{{completionStreak > 0}}">