fix: 缓存击穿/play竞态/onUnload泄漏/清除数据UI/统计NaN

- leaderboard 云函数: _fetchLatestByOpenid 加 in-flight promise,并发请求复用同一次扫描,防缓存击穿
- voice: play 加序列号,丢弃过期播放,避免旧语音截断新语音
- timer: onUnload 补取消 _completionCountUp,系统返回手势不再泄漏动画定时器
- settings: 清除数据 setData 补 voiceGender/vibrateIntensity 重置,避免 UI 与存储不一致
- storage: getTotalStats 对 r.duration 防御(Number||0),避免脏数据产生 NaN 传染

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

utils/voice.js

@@ -32,6 +32,7 @@ const FILEID_CACHE_KEY = 'tts_fileid_cache'
 const LOCAL_CACHE_KEY = 'tts_local_cache'   // { cacheKey: savedFilePath } - 持久本地文件,跨重启
 
 let _ctx = null
+let _playSeq = 0       // play 序列号,丢弃过期播放避免乱序
 let _localCache = null      // { cacheKey: savedFilePath } - persisted, lazy-loaded
 const _urlCache = {}        // { promptKey: audioUrl } — per-session, volatile
 let _fileIDCache = null     // { promptKey: fileID } — persisted, lazy-loaded
@@ -204,8 +205,11 @@ const preload = (keys) => {
  */
 const play = async (promptKey) => {
   if (!PROMPTS[promptKey]) return
+  const seq = ++_playSeq
   const src = await _resolveSrc(promptKey)
   if (!src) return
+  // 期间若有新的 play 调用,放弃本次,避免旧语音截断新语音
+  if (seq !== _playSeq) return
   const ctx = _getCtx()
   try {
     ctx.stop()