fix: 增强价格获取降级链日志

记录每个数据源的尝试和结果：
- [数据源获取开始]
- [数据源] 尝试 Yahoo/腾讯/Tiingo
- [数据源] Yahoo/腾讯/Tiingo 成功/失败
- 具体错误信息

帮助定位 UPRO 等股票获取失败的原因

AssetManager.Infrastructure/Services/MarketDataService.cs

@@ -104,13 +104,14 @@ public class MarketDataService : IMarketDataService
     /// </summary>
     private async Task<MarketPriceResponse> FetchPriceFromSourceAsync(string symbol, string assetType)
     {
-        _logger.LogInformation("从数据源获取价格: {Symbol}, 资产类型: {AssetType}", symbol, assetType);
+        _logger.LogInformation("[数据源获取开始] Symbol={Symbol}, AssetType={AssetType}", symbol, assetType);
         
         MarketPriceResponse response;
         string source;
         
         if (assetType.Equals("Crypto", StringComparison.OrdinalIgnoreCase))
         {
+            _logger.LogInformation("[数据源] 使用 OKX 获取 {Symbol}", symbol);
             response = await _okxService.GetCryptoPriceAsync(symbol);
             source = "OKX";
         }
@@ -119,22 +120,28 @@ public class MarketDataService : IMarketDataService
             // 股票：优先Yahoo财经，失败降级腾讯财经，最后降级 Tiingo
             try
             {
+                _logger.LogInformation("[数据源] 尝试 Yahoo 获取 {Symbol}", symbol);
                 response = await _yahooService.GetStockPriceAsync(symbol);
                 source = "Yahoo";
+                _logger.LogInformation("[数据源] Yahoo 成功: {Symbol} = {Price}", symbol, response.Price);
             }
             catch (Exception ex)
             {
-                _logger.LogWarning(ex, "Yahoo财经获取失败，降级使用 腾讯: {Symbol}", symbol);
+                _logger.LogWarning("[数据源] Yahoo 失败: {Symbol}, 错误: {Error}", symbol, ex.Message);
                 try
                 {
+                    _logger.LogInformation("[数据源] 降级使用腾讯获取 {Symbol}", symbol);
                     response = await _tencentService.GetStockPriceAsync(symbol);
                     source = "Tencent";
+                    _logger.LogInformation("[数据源] 腾讯成功: {Symbol} = {Price}", symbol, response.Price);
                 }
                 catch (Exception tencentEx)
                 {
-                    _logger.LogWarning(tencentEx, "腾讯财经获取失败，降级使用 Tiingo: {Symbol}", symbol);
+                    _logger.LogWarning("[数据源] 腾讯失败: {Symbol}, 错误: {Error}", symbol, tencentEx.Message);
+                    _logger.LogInformation("[数据源] 最后降级使用 Tiingo 获取 {Symbol}", symbol);
                     response = await _tiingoService.GetStockPriceAsync(symbol);
                     source = "Tiingo";
+                    _logger.LogInformation("[数据源] Tiingo 成功: {Symbol} = {Price}", symbol, response.Price);
                 }
             }
         }