fix: 修复多个金融计算问题

1. CreatePortfolioAsync: 初始建仓交易保存汇率信息
   - 设置 ExchangeRate 和 TotalAmountBase 字段
   - 支持跨币种初始建仓

2. ExchangeRateService: 增强 Mock 汇率降级
   - 扩展支持 EUR、GBP、JPY
   - 未知货币对记录 Error 级别日志

3. PositionItem: 增加 Shares 属性
   - 保留完整精度（解决 Amount int 截断问题）

AssetManager.Infrastructure/Services/ExchangeRateService.cs

@@ -116,11 +116,35 @@ public class ExchangeRateService : IExchangeRateService
             { "CNY-HKD", 1.09m },
             { "HKD-CNY", 0.92m },
             { "USD-HKD", 7.75m },
-            { "HKD-USD", 0.13m }
+            { "HKD-USD", 0.13m },
+            { "EUR-USD", 1.08m },
+            { "USD-EUR", 0.93m },
+            { "EUR-CNY", 7.70m },
+            { "CNY-EUR", 0.13m },
+            { "GBP-USD", 1.27m },
+            { "USD-GBP", 0.79m },
+            { "GBP-CNY", 9.00m },
+            { "CNY-GBP", 0.11m },
+            { "JPY-USD", 0.0067m },
+            { "USD-JPY", 149.50m },
+            { "JPY-CNY", 0.048m },
+            { "CNY-JPY", 20.90m }
         };
 
         string key = $"{fromCurrency.ToUpper()}-{toCurrency.ToUpper()}";
-        return Task.FromResult(mockRates.TryGetValue(key, out var rate) ? rate : 1.00m);
+        
+        if (mockRates.TryGetValue(key, out var rate))
+        {
+            _logger.LogWarning("Mock汇率命中: {Key} = {Rate}，计算结果可能不准确", key, rate);
+            return Task.FromResult(rate);
+        }
+        
+        // 未知货币对，记录严重警告
+        _logger.LogError("未知货币对，无法提供Mock汇率: {FromCurrency} -> {ToCurrency}，返回1.0可能导致计算错误", 
+            fromCurrency, toCurrency);
+        
+        // 返回1.0但记录严重警告，调用方应该检查日志
+        return Task.FromResult(1.00m);
     }
 }
 

AssetManager.Models/DTOs/PortfolioDTO.cs

@@ -90,7 +90,8 @@ public class PositionItem
     public string? StockCode { get; set; }
     public string? StockName { get; set; }
     public string? Symbol { get; set; }
-    public int Amount { get; set; }
+    public int Amount { get; set; } // 已弃用，保留兼容性
+    public double Shares { get; set; } // 完整精度的持仓数量
     public double AveragePrice { get; set; }
     public double CurrentPrice { get; set; }
     public double TotalValue { get; set; }

AssetManager.Services/PortfolioService.cs

@@ -138,7 +138,23 @@ public class PortfolioService : IPortfolioService
 
             _db.Insertable(position).ExecuteCommand();
 
-            // 创建交易记录
+            // 创建交易记录（保存汇率信息）
+            decimal totalAmount = (decimal)(stock.Price * stock.Amount);
+            decimal? exchangeRate = null;
+            decimal? totalAmountBase = null;
+            
+            // 如果持仓币种与组合币种不同，需要保存汇率
+            if (!string.IsNullOrEmpty(stock.Currency) && !stock.Currency.Equals(request.Currency, StringComparison.OrdinalIgnoreCase))
+            {
+                exchangeRate = await _exchangeRateService.GetExchangeRateAsync(stock.Currency, request.Currency);
+                totalAmountBase = totalAmount * exchangeRate.Value;
+            }
+            else
+            {
+                exchangeRate = 1.0m;
+                totalAmountBase = totalAmount;
+            }
+
             var transaction = new Transaction
             {
                 Id = "trans-" + Guid.NewGuid().ToString().Substring(0, 8),
@@ -149,8 +165,10 @@ public class PortfolioService : IPortfolioService
                 Title = "初始建仓",
                 Amount = (decimal)stock.Amount,
                 Price = (decimal)stock.Price,
-                TotalAmount = (decimal)(stock.Price * stock.Amount),
+                TotalAmount = totalAmount,
-                Currency = request.Currency,
+                Currency = stock.Currency ?? request.Currency,
+                ExchangeRate = exchangeRate,
+                TotalAmountBase = totalAmountBase,
                 Status = "completed",
                 Remark = "初始建仓",
                 TransactionTime = buyTime,
@@ -524,7 +542,8 @@ public class PortfolioService : IPortfolioService
                 StockCode = pos.StockCode,
                 StockName = pos.StockName,
                 Symbol = pos.StockCode,
-                Amount = (int)pos.Shares,
+                Amount = (int)pos.Shares, // 注意：此处精度丢失，仅用于显示
+                Shares = (double)pos.Shares, // 新增：保留完整精度
                 AveragePrice = (double)pos.AvgPrice,
                 CurrentPrice = (double)CurrentPrice,
                 TotalValue = (double)positionValueInTarget,