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

app.js

@@ -3,7 +3,7 @@ const cloud = require('./utils/cloud')
 const storage = require('./utils/storage')
 
 App({
-  onLaunch() {
+  async onLaunch() {
     // Init cloud storage (no-op if not configured)
     cloud.init()
 
@@ -28,14 +28,29 @@ App({
 
     this.globalData.theme = themeMod.getCurrentTheme()
 
-    // Sync with cloud: pull on empty local, push on non-empty local
+    // Sync with cloud: always locate our doc first (pullAll caches
+    // _openid / _docId), then either restore or push. The previous flow
+    // only pulled when local was empty, so on a cold start with non-empty
+    // local it pushed without locating — and because the module-level
+    // _openid / _docId caches had been reset, pushAll fell through to
+    // add() and created a duplicate cloud doc every cold start. The
+    // leaderboard then summed duration across N docs for the same user.
     const records = wx.getStorageSync('training_records')
-    if (!records || Object.keys(records).length === 0) {
-      // Case 1: Fresh install — restore from cloud
-      cloud.pullAll().then(cloudData => this._restoreFromCloud(cloudData))
-    } else {
-      // Case 2: Has local data — push to cloud (local is authoritative)
-      cloud.pushAll()
+    if (cloud.enabled) {
+      try {
+        const cloudData = await cloud.pullAll()
+        if (!records || Object.keys(records).length === 0) {
+          // Case 1: Fresh install (or user cleared local) — restore from cloud
+          this._restoreFromCloud(cloudData)
+        } else {
+          // Case 2: Has local data — push to cloud (local is authoritative)
+          // pullAll already populated _openid / _docId, so pushAll will
+          // update the existing doc instead of creating a duplicate.
+          cloud.pushAll()
+        }
+      } catch (e) {
+        console.error('Cloud sync on launch failed:', e)
+      }
     }
   },