fix: 行情获取失败时不写入错误数据，添加 429 限流重试机制

1. GetHistoricalPriceAsync 返回 decimal? 而非 decimal
   - 价格获取失败时返回 null 而非 0
2. BackfillNavHistoryInternalAsync 检查价格有效性
   - 任何持仓价格获取失败时跳过该日期
   - 不写入 totalValue=0 的错误数据
3. MarketDataService 添加 GetWithRetryAsync 方法
   - 处理 429 Too Many Requests 限流
   - 最多重试 3 次，指数退避

AssetManager.Infrastructure/Services/MarketDataService.cs

@@ -167,6 +167,40 @@ public class MarketDataService : IMarketDataService
         }
     }
 
+    /// <summary>
+    /// 带重试的 HTTP GET 请求（处理 429 限流）
+    /// </summary>
+    private async Task<HttpResponseMessage> GetWithRetryAsync(string url, int maxRetries = 3)
+    {
+        for (int i = 0; i < maxRetries; i++)
+        {
+            try
+            {
+                var response = await _httpClient.GetAsync(url);
+                
+                if (response.StatusCode == System.Net.HttpStatusCode.TooManyRequests)
+                {
+                    // 429 限流，等待后重试
+                    var retryAfter = response.Headers.RetryAfter?.Delta?.TotalSeconds ?? 2 * (i + 1);
+                    _logger.LogWarning("Tiingo API 限流，等待 {Seconds} 秒后重试 (第 {Attempt}/{Max} 次)", 
+                        retryAfter, i + 1, maxRetries);
+                    await Task.Delay((int)(retryAfter * 1000));
+                    continue;
+                }
+                
+                response.EnsureSuccessStatusCode();
+                return response;
+            }
+            catch (HttpRequestException ex) when (i < maxRetries - 1)
+            {
+                _logger.LogWarning(ex, "HTTP 请求失败，重试中 (第 {Attempt}/{Max} 次)", i + 1, maxRetries);
+                await Task.Delay(1000 * (i + 1));
+            }
+        }
+        
+        throw new HttpRequestException($"请求失败，已重试 {maxRetries} 次");
+    }
+
     /// <summary>
     /// 获取股票历史数据
     /// </summary>
@@ -185,15 +219,18 @@ public class MarketDataService : IMarketDataService
 
             // Tiingo 历史数据端点（和示例一致）
             var url = $"https://api.tiingo.com/tiingo/daily/{symbol}/prices?startDate={startDate:yyyy-MM-dd}&endDate={endDate:yyyy-MM-dd}&token={_tiingoApiKey}";
-            var response = await _httpClient.GetFromJsonAsync<List<TiingoDailyResponse>>(url);
+            
+            // 使用带重试的请求
+            var response = await GetWithRetryAsync(url);
+            var data = await response.Content.ReadFromJsonAsync<List<TiingoDailyResponse>>();
 
-            if (response == null)
+            if (data == null)
             {
                 return new List<MarketDataResponse>();
             }
 
             // 取最近 limit 条
-            var result = response
+            var result = data
                 .OrderByDescending(x => x.date)
                 .Take(limit)
                 .OrderBy(x => x.date)

AssetManager.Services/PortfolioNavService.cs

@@ -373,15 +373,34 @@ public class PortfolioNavService : IPortfolioNavService
 
             // 计算当日市值
             decimal totalValue = 0;
+            bool hasValidPrice = true;
+            List<string> failedSymbols = new List<string>();
+            
             foreach (var (stockCode, (shares, cost, currency, assetType)) in holdings)
             {
-                decimal price = await GetHistoricalPriceAsync(stockCode, assetType ?? "Stock", date);
+                var priceResult = await GetHistoricalPriceAsync(stockCode, assetType ?? "Stock", date);
+                if (priceResult == null || priceResult <= 0)
+                {
+                    hasValidPrice = false;
+                    failedSymbols.Add(stockCode);
+                    continue;
+                }
+                
+                decimal price = priceResult.Value;
                 decimal positionValue = shares * price;
                 decimal positionValueInTarget = await _exchangeRateService.ConvertAmountAsync(
                     positionValue, currency ?? targetCurrency, targetCurrency);
                 totalValue += positionValueInTarget;
             }
 
+            // 如果有任何持仓价格获取失败，跳过该日期，不写入错误数据
+            if (!hasValidPrice)
+            {
+                _logger.LogWarning("跳过日期 {Date}，以下持仓价格获取失败: {Symbols}", 
+                    date.ToString("yyyy-MM-dd"), string.Join(", ", failedSymbols));
+                continue;
+            }
+
             // 计算净值
             decimal nav = cumulativeCost > 0 ? totalValue / cumulativeCost : 1.0m;
             decimal cumulativeReturn = cumulativeCost > 0 ? (totalValue - cumulativeCost) / cumulativeCost * 100 : 0;
@@ -452,7 +471,7 @@ public class PortfolioNavService : IPortfolioNavService
     /// <summary>
     /// 获取历史价格
     /// </summary>
-    private async Task<decimal> GetHistoricalPriceAsync(string symbol, string assetType, DateTime date)
+    private async Task<decimal?> GetHistoricalPriceAsync(string symbol, string assetType, DateTime date)
     {
         try
         {
@@ -478,12 +497,19 @@ public class PortfolioNavService : IPortfolioNavService
 
             // 最后尝试获取实时价格
             var currentPrice = await _marketDataService.GetPriceAsync(symbol, assetType);
-            return currentPrice.Price;
+            if (currentPrice != null && currentPrice.Price > 0)
+            {
+                return currentPrice.Price;
+            }
+
+            // 无法获取有效价格
+            _logger.LogWarning("无法获取有效价格: {Symbol}, {Date}", symbol, date);
+            return null;
         }
         catch (Exception ex)
         {
             _logger.LogWarning(ex, "获取历史价格失败: {Symbol}, {Date}", symbol, date);
-            return 0;
+            return null;
         }
     }