feat(timer): 训练中轮换姿势要领 + hint 字号调大

- 训练中 hint 每 12 秒轮换一条平板支撑姿势要领(收紧核心/肩膀放松/
  别塌腰/别憋气等 10 条),替代固定文案,帮助持续纠正姿势
- 姿势文案与间隔移入 config.js(postureTips/tipInterval),统一管理
- hint 字号 28rpx -> 34rpx,图标 32rpx -> 36rpx,更易看清

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pages/timer/timer.js

@@ -5,7 +5,7 @@ const themeMod = require('../../utils/theme')
 const iconsMod = require('../../utils/icons')
 const voice = require('../../utils/voice')
 const { countUp } = require('../../utils/countUp')
-
+const config = require('../../config')
 Page({
   data: {
     theme: { primary: '#FF6B35', primaryLight: '#FF8C5A', primaryBg: '#FFF3ED', primaryRgb: '255,107,53' },
@@ -18,6 +18,7 @@ Page({
     isCompleted: false,
     overtime: 0,
     goalReached: false,
+    hintTip: (config.postureTips && config.postureTips[0]) || '',
     todayTarget: 0,
     planDay: 1,
     isFreeMode: false,
@@ -96,6 +97,7 @@ Page({
     this._lastMinuteAt = 0
     this._lastCountdown = 0
     this._saving = false
+    this._lastTipIndex = -1
     this._clearVibrateTimers()
 
     this._timer = new Timer({
@@ -104,6 +106,7 @@ Page({
           remaining: tick.remaining > 0 ? tick.remaining : 0,
           overtime: tick.remaining <= 0 ? tick.elapsed - this.data.duration : 0
         })
+        this._updateHintTip(tick)
         this._remind(tick)
       },
       onGoalReached: () => {
@@ -118,6 +121,24 @@ Page({
     })
   },
 
+  /**
+   * Rotate the posture cue in the hint area every config.tipInterval seconds.
+   * Only runs while still under the target (after goalReached the hint
+   * switches to the "goal reached" line). Skips setData when the index
+   * hasn't changed to avoid per-second re-renders.
+   */
+  _updateHintTip(tick) {
+    if (tick.remaining <= 0) return
+    const tips = config.postureTips || []
+    if (tips.length === 0) return
+    const interval = config.tipInterval || 12
+    const idx = Math.floor(tick.elapsed / interval) % tips.length
+    if (idx !== this._lastTipIndex) {
+      this._lastTipIndex = idx
+      this.setData({ hintTip: tips[idx] })
+    }
+  },
+
   /**
    * Per-tick reminders: vibration + voice prompts at 4 fixed points.
    * - halfway: once when elapsed reaches half of duration
@@ -431,6 +452,7 @@ Page({
     this._last10Signaled = false
     this._lastMinuteAt = 0
     this._lastCountdown = 0
+    this._lastTipIndex = -1
     this._clearVibrateTimers()
     this.setData({
       showCompletion: false,