feat(ui): 记录页月份联动与多项 UI 美化/修复

- records: 底部列表与月份选择器联动，新增 [本月|最近] 分段控件；标题/空态随模式切换
- leaderboard: 领奖台布局(冠军居中+皇冠)、次数标注于底座且三档水平对齐；头像 cloud:// 批量预解析提速(云函数需重新部署)
- index/timer: 主色底图标改白色变体修复隐形；目标数字按微信字体缩放补偿真机遮挡
- settings: 配色方案横滑渐变色卡；头像上传前压缩至 200px
- theme: 新增 teal 主题；暗黑背景统一对齐
- 圆形头像双保险(image 自身 border-radius)修复月/年榜方图

注: cloudfunctions/leaderboard 改动须在开发者工具重新部署才生效。

utils/timer.js

@@ -36,14 +36,25 @@ class Timer {
     this._tick()
     this._intervalId = setInterval(() => { this._tick() }, 1000)
 
-    // Register foreground listener (idempotent — we keep a flag so we don't
+    // Register foreground listener (idempotent — keep a flag so we don't
     // double-register if start() is called multiple times in one session)
-    if (!this._appShowBound && typeof wx.onAppShow === 'function') {
-      try {
-        wx.onAppShow(this._onAppShow)
-        this._appShowBound = true
-      } catch (e) {}
-    }
+    this._bindAppShow()
+  }
+
+  _bindAppShow() {
+    if (this._appShowBound || typeof wx.onAppShow !== 'function') return
+    try {
+      wx.onAppShow(this._onAppShow)
+      this._appShowBound = true
+    } catch (e) {}
+  }
+
+  _unbindAppShow() {
+    if (!this._appShowBound || typeof wx.offAppShow !== 'function') return
+    try {
+      wx.offAppShow(this._onAppShow)
+    } catch (e) {}
+    this._appShowBound = false
   }
 
   pause() {
@@ -67,6 +78,7 @@ class Timer {
     this._paused = false
     clearInterval(this._intervalId)
     this._intervalId = null
+    this._unbindAppShow()
     return this._elapsed
   }