feat(ui): 排行榜与首页打卡卡片多项优化

排行榜性能:
- 客户端乐观缓存:进页面/切周期秒显旧数据,后台静默刷新,消除 2-3s 空白
- 云函数实例缓存 TTL 60s -> 5min,降低全表扫描频率

排行榜 UI:
- 空状态重设计:奖杯光环插画(径向光晕 + 闪光漂浮)
- 领奖台 slot 撑满对齐列表、金银铜底座配色、角标与昵称间距修复、底线对齐

首页打卡卡片:
- 火焰光晕脉动 + 72rpx 大数字 + 分段进度格子
- 计划 >10 天时进度退化为里程碑连续条

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

utils/storage.js

@@ -418,6 +418,43 @@ const getTodayRecord = () => {
   return hasRecord ? { date: today, duration: totalDuration } : null
 }
 
+/**
+ * Leaderboard display cache, keyed by period ('day' | 'month' | 'year').
+ *
+ * Why: building the board requires a full-collection scan in the cloud
+ * function (cursor-paginated 100/page, serial), which takes 2-3s when
+ * the function's in-instance cache is cold. This client cache lets the
+ * page paint the last-rendered result instantly on re-entry / period
+ * switch while the cloud refreshes in the background.
+ *
+ * Freshness: entries older than LB_CACHE_MAX_AGE are treated as misses -
+ * the cached avatarUrl is a cloud:// temp URL (~2h TTL) and stale links
+ * render as broken images. 30min stays safely inside that window while
+ * still covering the common "switch tab / switch period" re-entry case.
+ */
+const LEADERBOARD_CACHE_KEY = 'leaderboard_cache'
+const LB_CACHE_MAX_AGE = 30 * 60 * 1000
+
+const getLeaderboardCache = (period) => {
+  if (!period) return null
+  try {
+    const all = wx.getStorageSync(LEADERBOARD_CACHE_KEY) || {}
+    const entry = all[period]
+    if (!entry) return null
+    if (Date.now() - (entry.cachedAt || 0) > LB_CACHE_MAX_AGE) return null
+    return entry
+  } catch (e) { return null }
+}
+
+const setLeaderboardCache = (period, payload) => {
+  if (!period || !payload) return
+  try {
+    const all = wx.getStorageSync(LEADERBOARD_CACHE_KEY) || {}
+    all[period] = { ...payload, cachedAt: Date.now() }
+    wx.setStorageSync(LEADERBOARD_CACHE_KEY, all)
+  } catch (e) {}
+}
+
 module.exports = {
   getRecords,
   saveRecord,
@@ -439,5 +476,7 @@ module.exports = {
   _markLocalChanged,
   getToday,
   getDateOffset,
-  getTodayRecord
+  getTodayRecord,
+  getLeaderboardCache,
+  setLeaderboardCache
 }