fix(ledger): 修復平均成本顯示 Bug，並優化分紅獨立統計邏輯

Memory.md

@@ -54,4 +54,9 @@
 - 重構了分紅的會計處理邏輯，將其正確計入已實現盈虧：DIVIDEND 不再增加持倉數量，而是按 `quantity * price * exchangeRate` 計算分紅金額並累加至 `realizedPnlCny`。
 - 新增 `totalDividendCny` 字段追蹤累計分紅金額。
 - 修正攤薄成本算法：`dilutedCost = (totalBuyCostCny - realizedPnlCny - totalDividendCny) / currentQuantity`，確保極端情況下攤薄成本為負數時精確返回負數，絕不兜底為 0。
-- 平均成本 `avgCost = totalBuyCostCny / totalBuyQuantity` 保持不變，僅在遍歷結束後計算。
+- 平均成本 `avgCost = totalBuyCostCny / totalBuyQuantity` 保持不變，僅在遍歷結束後計算。
+
+## 修復平均成本顯示 Bug與分紅獨立統計 (Task 35)
+- 修復了平均成本在前端顯示為空的問題：`totalBuyQuantity` 在 BUY 交易處理中從未累加，導致 `avgCost` 計算時除數為零而永遠返回 0。現在在 BUY 時正確執行 `totalBuyQuantity += quantity`。
+- 將分紅邏輯從已實現盈虧中剝離，建立獨立的累計分紅統計維度：新增 `accumulatedDividendsCny` 字段，DIVIDEND 交易不再混入 `realizedPnlCny`，而是獨立累加至 `accumulatedDividendsCny`。
+- 重新定義總盈虧公式：`totalPnlCny = unrealizedPnlCny + realizedPnlCny + accumulatedDividendsCny`，確保分紅有獨立的統計維度且不會干擾平均成本計算。

src/actions/portfolio.ts

@@ -25,7 +25,7 @@ interface Position {
   dilutedCost: string;
   holdingDays: number;
   exchange: string;
-  totalDividendCny: string;
+  accumulatedDividendsCny: string;
 }
 
 interface RawRate {
@@ -158,6 +158,7 @@ export async function getPortfolioPositions(): Promise<Position[]> {
     totalBuyQuantity: Big;
     // 已实现盈亏
     realizedPnlCny: Big;
+    accumulatedDividendsCny: Big;
     // 首次买入日期
     firstBuyDate: Date | null;
   }>();
@@ -180,7 +181,7 @@ export async function getPortfolioPositions(): Promise<Position[]> {
         totalBuyCostNative: new Big('0'),
         totalBuyQuantity: new Big('0'),
         realizedPnlCny: new Big('0'),
-        totalDividendCny: new Big('0'),
+        accumulatedDividendsCny: new Big('0'),
         firstBuyDate: null,
       });
     }
@@ -200,6 +201,7 @@ export async function getPortfolioPositions(): Promise<Position[]> {
       }
       const costCny = costPerUnit.times(new Big(appliedRate || '1'));
       holding.totalBuyCostCny = holding.totalBuyCostCny.plus(costCny);
+      holding.totalBuyQuantity = holding.totalBuyQuantity.plus(new Big(tx.quantity));
 
       // 记录首次买入日期
       if (!holding.firstBuyDate && tx.executedAt) {
@@ -232,8 +234,7 @@ export async function getPortfolioPositions(): Promise<Position[]> {
     } else if (tx.txType === 'DIVIDEND') {
       const dividendAmountNative = new Big(tx.quantity).times(new Big(tx.price));
       const dividendCny = dividendAmountNative.times(new Big(tx.exchangeRate || '1'));
-      holding.realizedPnlCny = holding.realizedPnlCny.plus(dividendCny);
+      holding.accumulatedDividendsCny = holding.accumulatedDividendsCny.plus(dividendCny);
-      holding.totalDividendCny = holding.totalDividendCny.plus(dividendCny);
     }
 
     if (tx.assetLatestPrice) {
@@ -256,8 +257,8 @@ export async function getPortfolioPositions(): Promise<Position[]> {
 
     // 未实现盈亏 = 当前市值 - 总买入成本
     const unrealizedPnlCny = cnyValue.minus(holding.totalBuyCostCny);
-    // 总盈亏 = 未实现盈亏 + 已实现盈亏
+    // 总盈亏 = 当前市值 - 总买入成本 + 已实现盈亏 + 累计分红
-    const totalPnlCny = unrealizedPnlCny.plus(holding.realizedPnlCny);
+    const totalPnlCny = unrealizedPnlCny.plus(holding.realizedPnlCny).plus(holding.accumulatedDividendsCny);
 
     const currentNativeValue = new Big(holding.latestPrice).times(holding.quantity);
     const pnlNative = currentNativeValue.minus(holding.totalBuyCostNative);
@@ -271,7 +272,7 @@ export async function getPortfolioPositions(): Promise<Position[]> {
     // 摊薄成本 = (总买入成本 - 已实现盈亏 - 总分红) / 当前持仓数量
     let dilutedCost = new Big('0');
     if (holding.quantity.gt(0)) {
-      dilutedCost = holding.totalBuyCostCny.minus(holding.realizedPnlCny).minus(holding.totalDividendCny).div(holding.quantity);
+      dilutedCost = holding.totalBuyCostCny.minus(holding.realizedPnlCny).minus(holding.accumulatedDividendsCny).div(holding.quantity);
     }
 
     // 持仓天数
@@ -300,7 +301,7 @@ export async function getPortfolioPositions(): Promise<Position[]> {
       dilutedCost: dilutedCost.toString(),
       holdingDays,
       exchange: holding.exchange,
-      totalDividendCny: holding.totalDividendCny.toString(),
+      accumulatedDividendsCny: holding.accumulatedDividendsCny.toString(),
     });
   }