feat(排行榜): 实现动态数据加载并添加日期显示

- 重构排行榜组件，从API动态加载数据
- 添加排行榜日期显示功能
- 优化区域切换逻辑，支持动态区域显示
- 调整返回顶部按钮位置
- 添加默认头像处理逻辑

 <!--
  * @Date: 2025-09-02 13:06:39
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2025-09-02 13:12:20
+ * @LastEditTime: 2025-09-09 14:17:13
  * @FilePath: /lls_program/src/components/BackToTop.vue
  * @Description: 文件描述
 -->
@@ -56,7 +56,7 @@ const scrollToTop = () => {
 .back-to-top {
   position: fixed;
   right: 30rpx;
-  bottom: 180rpx;
+  bottom: 250rpx;
   width: 80rpx;
   height: 80rpx;
   background: rgba(64, 158, 255, 0.8);

 <!--
  * @Date: 2025-09-01 13:07:52
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2025-09-09 14:07:23
+ * @LastEditTime: 2025-09-09 14:16:08
  * @FilePath: /lls_program/src/pages/FamilyRank/index.vue
  * @Description: 文件描述
 -->
@@ -34,6 +34,11 @@
         <view class="loading-text">加载中...</view>
       </view>
 
+      <!-- 排行榜日期 -->
+      <view class="rank-date">
+        {{ currentDate }}
+      </view>
+
       <!-- 前三名展示 -->
       <view v-else-if="topThreeData.length > 0" class="top-three">
         <!-- 第二名 -->
@@ -131,7 +136,7 @@
     </view>
 
     <!-- 返回顶部组件 -->
-    <!-- <BackToTop :distance="200" /> -->
+    <BackToTop :distance="200" />
   </view>
 </template>
 
@@ -165,7 +170,8 @@ const leaderboardData = ref(null)
 // 加载状态
 const loading = ref(false)
 
-
+// 当前日期
+const currentDate = ref('')
 
 /**
  * 切换tab
@@ -230,6 +236,7 @@ const loadLeaderboardData = async (isInitialLoad = false) => {
     const response = await getStepLeaderboardAPI(params)
     if (response.code) {
       leaderboardData.value = response.data
+      currentDate.value = response.data.yesterday
 
       // 只在初始加载时从current_family.county获取区县信息，设置默认tab
       if (isInitialLoad && response.data.current_family) {
@@ -411,6 +418,14 @@ onMounted(async () => {
       opacity: 0.3;
       transform: translateY(-20rpx);
     }
+
+    .rank-date {
+      font-size: 28rpx;
+      color: rgba(255, 255, 255, 0.8);
+      text-align: center;
+      margin-top: 40rpx;
+      margin-bottom: 40rpx;
+    }
   }
 
   .top-three {