refactor: 简化收益曲线顶部指标

- 移除涨跌比例（与下方总收益重复）
- 保留最新净值数字，布局更简洁
- 放大净值字体 44rpx -> 48rpx

pages/detail/detail.vue

@@ -87,15 +87,9 @@
         <view v-else class="nav-chart-wrapper">
           <!-- 净值指标 -->
           <view class="nav-indicator">
-            <view class="indicator-main">
             <text class="indicator-label">最新净值</text>
             <text class="indicator-value">{{ (navHistory[navHistory.length - 1]?.nav || 1).toFixed(4) }}</text>
           </view>
-            <view class="indicator-change" :class="navStatistics?.totalReturn >= 0 ? 'positive' : 'negative'">
-              <text class="change-arrow">{{ navStatistics?.totalReturn >= 0 ? '↑' : '↓' }}</text>
-              <text class="change-value">{{ Math.abs(navStatistics?.totalReturn || 0).toFixed(2) }}%</text>
-            </view>
-          </view>
           
           <!-- 图表区域 -->
           <view class="chart-area">
@@ -1376,18 +1370,12 @@ const deletePortfolio = async () => {
 
 /* 净值指标 */
 .nav-indicator {
-  display: flex;
-  justify-content: space-between;
-  align-items: flex-start;
-  padding: 16rpx 0 24rpx;
-  border-bottom: 1rpx solid #F3F4F6;
-  margin-bottom: 16rpx;
-}
-
-.indicator-main {
   display: flex;
   flex-direction: column;
   gap: 8rpx;
+  padding: 12rpx 0 16rpx;
+  border-bottom: 1rpx solid #F3F4F6;
+  margin-bottom: 12rpx;
 }
 
 .indicator-label {
@@ -1396,50 +1384,12 @@ const deletePortfolio = async () => {
 }
 
 .indicator-value {
-  font-size: 44rpx;
+  font-size: 48rpx;
   font-weight: 700;
   font-family: 'DIN Alternate', sans-serif;
   color: #1F2937;
 }
 
-.indicator-change {
-  display: flex;
-  align-items: center;
-  gap: 4rpx;
-  padding: 8rpx 16rpx;
-  border-radius: 8rpx;
-  margin-top: 8rpx;
-}
-
-.indicator-change.positive {
-  background-color: #ECFDF5;
-}
-
-.indicator-change.negative {
-  background-color: #FEF2F2;
-}
-
-.change-arrow {
-  font-size: 28rpx;
-  font-weight: 600;
-}
-
-.indicator-change.positive .change-arrow,
-.indicator-change.positive .change-value {
-  color: #059669;
-}
-
-.indicator-change.negative .change-arrow,
-.indicator-change.negative .change-value {
-  color: #DC2626;
-}
-
-.change-value {
-  font-size: 28rpx;
-  font-weight: 600;
-  font-family: 'DIN Alternate', sans-serif;
-}
-
 /* 图表区域 */
 .chart-area {
   width: 100%;