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>

cloudfunctions/leaderboard/index.js

@@ -22,6 +22,7 @@ const TZ_OFFSET_MS = 8 * 60 * 60 * 1000
 // across instances, which is fine - the board needn't be real-time.
 const CACHE_TTL = 60 * 1000
 let _docsCache = null  // { latestByOpenid: Map, ts }
+let _docsCachePromise = null  // in-flight 扫描 promise,防缓存击穿
 
 const tsOf = (d) => {
   if (!d.updatedAt) return 0
@@ -40,6 +41,9 @@ const _fetchLatestByOpenid = async () => {
   if (_docsCache && (Date.now() - _docsCache.ts) < CACHE_TTL) {
     return _docsCache.latestByOpenid
   }
+  // 缓存过期:复用 in-flight promise,避免并发请求各自全表扫描(缓存击穿)
+  if (_docsCachePromise) return _docsCachePromise
+  _docsCachePromise = (async () => {
   const latestByOpenid = new Map()
   // Exclude accounts that haven't synced in 90+ days to bound the scan.
   // Docs without an updatedAt field (pre-fix legacy) are included as well.
@@ -66,6 +70,8 @@ const _fetchLatestByOpenid = async () => {
   }
   _docsCache = { latestByOpenid, ts: Date.now() }
   return latestByOpenid
+  })()
+  try { return await _docsCachePromise } finally { _docsCachePromise = null }
 }
 
 exports.main = async (event) => {