feat: 完成训练分级庆祝 (normal/first/milestone/record)

- normal: 12 条彩带
- record (破个人纪录): 24 条 + 横幅"🏆 新纪录!X秒"
- milestone (连击 7/14/30/50/100/365 天): 32 条 + 横幅
- first (首次训练): 40 条 + 横幅"🎉 第一次训练"

横幅 3.5s 后自动淡出,彩带时长随等级递增(2.4s → 4s)。

pages/timer/timer.js

@@ -20,6 +20,9 @@ Page({
     todayTarget: 0,
     planDay: 1,
     isFreeMode: false,
+    celebrationLevel: 'normal',  // normal / first / milestone / record
+    celebrationMessage: '',
+    confettiPieces: [],
     icons: iconsMod.build()
   },
 
@@ -92,7 +95,16 @@ Page({
         this._remind(tick)
       },
       onComplete: () => {
-        this.setData({ status: 'completed', isCompleted: true })
+        const elapsed = this._timer.elapsed
+        const { level, message } = this._detectCelebrationLevel(elapsed)
+        const confettiPieces = this._buildConfettiPieces(level)
+        this.setData({
+          status: 'completed',
+          isCompleted: true,
+          celebrationLevel: level,
+          celebrationMessage: message,
+          confettiPieces
+        })
         const s = storage.getSettings()
         if (s.vibrate) {
           try { wx.vibrateLong() } catch (e) {}
@@ -162,6 +174,53 @@ Page({
     }
   },
 
+  /**
+   * Detect which celebration level to show. Called at onComplete (BEFORE
+   * saveRecord fires in finishTraining), so stats reflect pre-save state.
+   *  - first:     user's very first training ever
+   *  - milestone: streak will hit a memorable number after this save
+   *  - record:    this duration beats the user's previous max
+   *  - normal:    everything else
+   */
+  _detectCelebrationLevel(elapsed) {
+    const stats = storage.getTotalStats()
+    const streak = storage.getStreak()
+    const nextStreak = (streak.lastDate && streak.count >= 1) ? streak.count + 1 : 1
+
+    if (stats.totalSessions === 0) {
+      return { level: 'first', message: '🎉 第一次训练!坚持就是胜利' }
+    }
+    if ([7, 14, 30, 50, 100, 365].includes(nextStreak)) {
+      return { level: 'milestone', message: `🔥 连续打卡 ${nextStreak} 天!` }
+    }
+    if (elapsed > stats.maxDuration) {
+      return { level: 'record', message: `🏆 新纪录!${elapsed}秒` }
+    }
+    return { level: 'normal', message: '完成!' }
+  },
+
+  /**
+   * Build the confetti piece list. More pieces + more colors for higher
+   * celebration levels. Pieces are pre-positioned so the layout doesn't
+   * shift when wx:for renders them.
+   */
+  _buildConfettiPieces(level) {
+    const counts = { normal: 12, record: 24, milestone: 32, first: 40 }
+    const count = counts[level] || counts.normal
+    const palette = ['#FF6B35', '#FFD93D', '#4CAF50', '#2979FF', '#EC407A', '#7E57C2', '#FF8C5A', '#5C9CFF', '#6EC072', '#A08AD6']
+    const pieces = []
+    for (let i = 0; i < count; i++) {
+      pieces.push({
+        left: Math.round((i / count) * 96 + 2),
+        color: palette[i % palette.length],
+        delay: Math.round(Math.random() * 300) / 1000,
+        rotate: Math.round((Math.random() * 90) - 45),
+        size: level === 'first' ? 40 : level === 'milestone' ? 36 : 32
+      })
+    }
+    return pieces
+  },
+
   onUnload() {
     voice.stop()
     voice.destroy()