修复行情缓存字段溢出问题：价格保留8位小数，字段长度扩展为20位

AssetManager.Data/MarketPriceCache.cs

@@ -29,13 +29,13 @@ public class MarketPriceCache
     /// <summary>
     /// 最新价格
     /// </summary>
-    [SugarColumn(DecimalDigits = 8, IsNullable = false)]
+    [SugarColumn(Length = 20, DecimalDigits = 8, IsNullable = false)]
     public decimal Price { get; set; }
 
     /// <summary>
     /// 前收盘价（计算当日涨跌幅用）
     /// </summary>
-    [SugarColumn(DecimalDigits = 8, IsNullable = true)]
+    [SugarColumn(Length = 20, DecimalDigits = 8, IsNullable = true)]
     public decimal? PreviousClose { get; set; }
 
     /// <summary>

AssetManager.Infrastructure/Services/MarketDataService.cs

@@ -342,14 +342,14 @@ public class MarketDataService : IMarketDataService
             source = "Tiingo";
         }
 
-        // 写入缓存
+        // 写入缓存，保留8位小数，避免字段超出范围
         var cacheEntity = new MarketPriceCache
         {
             Id = cacheKey,
             Symbol = symbol.ToUpper(),
             AssetType = assetType.ToUpper(),
-            Price = response.Price,
-            PreviousClose = response.PreviousClose,
+            Price = Math.Round(response.Price, 8),
+            PreviousClose = response.PreviousClose > 0 ? Math.Round(response.PreviousClose, 8) : null,
             Source = source,
             FetchedAt = DateTime.Now,
             ExpiredAt = GetCacheExpirationTime(assetType)