fix: 修复排行榜数据自增长（冷启动重复创建云端文档）

每次小程序冷启动都会为同一用户创建新的云端文档，
导致 leaderboard 把同一份数据累加 N 次。

改动：
- app.js: onLaunch 改为 async，每次启动先 pullAll 填充 _openid / _docId 缓存
- utils/cloud.js: 引入 _ensureOpenid() 单次解析；_doPush 总是先按 openid
  定位现有文档；update 失败不再回退到 add()（避免创建重复文档）
- utils/storage.js: getTodayRecord 按日期部分比较，修复一天第二次训练

utils/storage.js

@@ -245,12 +245,18 @@ const getDateOffset = (dateStr, offset) => {
 
 const getTodayRecord = () => {
   const today = getToday()
+  // Record `date` is "YYYY-MM-DD HH:MM:SS" (formatted at saveRecord time),
+  // so a strict === check against the freshly-formatted `today` only matches
+  // a record saved in the exact same second. Compare date-only portions
+  // instead, otherwise the second training of the day reads as zero and
+  // the home page flips "今日已完成" back off.
+  const todayOnly = dateOnly(today)
   const records = getRecords()
   let totalDuration = 0
   let hasRecord = false
   Object.keys(records).forEach((month) => {
     records[month].forEach((r) => {
-      if (r.date === today) {
+      if (dateOnly(r.date) === todayOnly) {
         totalDuration += r.duration
         hasRecord = true
       }