fix: seed existing local data to cloud on first launch

Previously cloud sync only triggered on writes. If the user already
had training records before cloud was enabled, they'd never be pushed
— leaving the database empty until the next training session.

Now onLaunch handles both cases:
  - Local empty → restore from cloud (recovery after deletion)
  - Local has data → check cloud; if cloud empty, push existing data up

Also extract _restoreFromCloud to reduce nesting.

app.js

@@ -24,10 +24,26 @@ App({
 
     this.globalData.theme = themeMod.getCurrentTheme()
 
-    // If local records are empty, try pulling from cloud
+    // Sync with cloud: pull on empty local, push on empty cloud
     const records = wx.getStorageSync('training_records')
     if (!records || Object.keys(records).length === 0) {
-      cloud.pullAll().then((cloudData) => {
+      // Case 1: Fresh install — restore from cloud
+      cloud.pullAll().then(cloudData => this._restoreFromCloud(cloudData))
+    } else {
+      // Case 2: Has local data — check if cloud needs seeding
+      cloud.pullAll().then(cloudData => {
+        if (!cloudData) {
+          // Cloud empty: push existing local data up
+          cloud.pushAll()
+        } else {
+          // Both have data — trust local (latest) and re-push
+          cloud.pushAll()
+        }
+      })
+    }
+  },
+
+  _restoreFromCloud(cloudData) {
     if (!cloudData) return
     try {
       if (cloudData.records && Object.keys(cloudData.records).length > 0) {
@@ -45,8 +61,6 @@ App({
     } catch (e) {
       console.error('Cloud restore failed:', e)
     }
-      })
-    }
   },
 
   globalData: {