perf(voice): app onLaunch 预载语音,进一步消除首段延迟

- app.js onLaunch 调 voice.preload(),app 启动即后台下载全部语音
- 与 timer 页 onLoad 预载形成双保险(已缓存条目 no-op)
- 仅语音引导开启时预载,在 cloud.init 之后调用

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

app.js

@@ -2,6 +2,7 @@ const themeMod = require('./utils/theme')
 const cloud = require('./utils/cloud')
 const storage = require('./utils/storage')
 const darkMod = require('./utils/darkMode')
+const voice = require('./utils/voice')
 
 App({
   async onLaunch() {
@@ -46,6 +47,10 @@ App({
       wx.setStorageSync('user_settings', settings)
     }
 
+    // 预载语音到本地缓存:app 启动即后台下载,训练时即时播放(语音引导开启时)
+    const _vs = wx.getStorageSync('user_settings') || {}
+    if (_vs.voiceGuide !== false) voice.preload()
+
     const streak = wx.getStorageSync('current_streak')
     if (!streak) {
       wx.setStorageSync('current_streak', { count: 0, lastDate: '' })