feat: 收益曲线优化

1. 修复 Canvas 实例，添加 this 参数
2. 曲线颜色随收益正负变化（绿涨红跌）
3. 空状态增加回填按钮，引导用户生成收益曲线

pages/detail/detail.vue

@@ -77,6 +77,10 @@
         <!-- 无数据 -->
         <view v-else-if="!navHistory || navHistory.length === 0" class="nav-empty">
           <text class="empty-text">暂无收益数据</text>
+          <text class="empty-hint">回填历史净值后可生成收益曲线</text>
+          <button class="backfill-btn" @click="handleBackfillNav" :disabled="backfillLoading">
+            {{ backfillLoading ? '回填中...' : '生成收益曲线' }}
+          </button>
         </view>
         
         <!-- 收益曲线 -->
@@ -480,6 +484,7 @@ const navLoading = ref(false);
 const navPeriod = ref('30d');
 const navHistory = ref([]);
 const navStatistics = ref(null);
+const backfillLoading = ref(false);
 
 // 绘制收益曲线
 const drawNavChart = () => {
@@ -487,7 +492,7 @@ const drawNavChart = () => {
   if (!data || data.length === 0) return;
   
   nextTick(() => {
-    const ctx = uni.createCanvasContext('navChart');
+    const ctx = uni.createCanvasContext('navChart', this);
     
     // 画布尺寸 (rpx -> px)
     const width = 320;
@@ -502,6 +507,12 @@ const drawNavChart = () => {
     const maxVal = Math.max(...values) * 1.02;
     const range = maxVal - minVal || 1;
     
+    // 判断收益正负，决定颜色
+    const totalReturn = navStatistics.value?.totalReturn || 0;
+    const isPositive = totalReturn >= 0;
+    const lineColor = isPositive ? '#059669' : '#DC2626';
+    const fillColor = isPositive ? 'rgba(5, 150, 105, 0.15)' : 'rgba(220, 38, 38, 0.15)';
+    
     // 清空画布
     ctx.clearRect(0, 0, width, height);
     
@@ -541,12 +552,12 @@ const drawNavChart = () => {
     ctx.lineTo(points[points.length - 1].x, padding.top + chartHeight);
     ctx.lineTo(points[0].x, padding.top + chartHeight);
     ctx.closePath();
-    ctx.setFillStyle('rgba(6, 78, 59, 0.15)');
+    ctx.setFillStyle(fillColor);
     ctx.fill();
     
     // 绘制曲线
     ctx.beginPath();
-    ctx.setStrokeStyle('#064E3B');
+    ctx.setStrokeStyle(lineColor);
     ctx.setLineWidth(2);
     points.forEach((p, i) => {
       if (i === 0) ctx.moveTo(p.x, p.y);
@@ -571,6 +582,32 @@ const drawNavChart = () => {
   });
 };
 
+// 回填净值历史
+const handleBackfillNav = async () => {
+  if (!portfolioId.value) return;
+  
+  backfillLoading.value = true;
+  try {
+    const response = await api.assets.backfillNavHistory(portfolioId.value, true);
+    if (response.code === 200) {
+      uni.showToast({
+        title: `成功生成 ${response.data.recordsCreated} 条记录`,
+        icon: 'success'
+      });
+      // 重新获取净值历史
+      await fetchNavHistory();
+    }
+  } catch (error) {
+    console.error('回填净值失败:', error);
+    uni.showToast({
+      title: '生成失败，请重试',
+      icon: 'none'
+    });
+  } finally {
+    backfillLoading.value = false;
+  }
+};
+
 // 交易表单
 const showTransactionForm = ref(false);
 const transactionType = ref('buy'); // buy 或 sell
@@ -1323,9 +1360,11 @@ const deletePortfolio = async () => {
 .nav-loading,
 .nav-empty {
   display: flex;
+  flex-direction: column;
   align-items: center;
   justify-content: center;
   height: 400rpx;
+  gap: 16rpx;
 }
 
 .loading-text,
@@ -1334,6 +1373,26 @@ const deletePortfolio = async () => {
   color: #9CA3AF;
 }
 
+.empty-hint {
+  font-size: 24rpx;
+  color: #D1D5DB;
+  margin-bottom: 8rpx;
+}
+
+.backfill-btn {
+  margin-top: 16rpx;
+  padding: 16rpx 32rpx;
+  font-size: 26rpx;
+  color: #FFFFFF;
+  background-color: #059669;
+  border-radius: 8rpx;
+  border: none;
+}
+
+.backfill-btn[disabled] {
+  background-color: #9CA3AF;
+}
+
 .nav-chart-wrapper {
   position: relative;
   width: 100%;