feat(leaderboard): 下拉刷新动画图标

下拉刷新时顶部显示主题色旋转 spinner + "刷新中…"指示器,
仅下拉刷新显示(pullRefreshing),后台静默刷新保持无感。

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

pages/leaderboard/leaderboard.js

@@ -18,6 +18,7 @@ Page({
     myEntry: null,
     loading: false,
     refreshing: false,
+    pullRefreshing: false,
     empty: false,
     icons: iconsMod.build()
   },
@@ -48,7 +49,11 @@ Page({
   },
 
   onPullDownRefresh() {
-    this.fetchRank(() => wx.stopPullDownRefresh(), true)
+    this.setData({ pullRefreshing: true })
+    this.fetchRank(() => {
+      this.setData({ pullRefreshing: false })
+      wx.stopPullDownRefresh()
+    }, true)
   },
 
   switchPeriod(e) {