feat(portfolio): 支持显示已清仓历史持仓，增加防乱码 CSV 导出功能

Memory.md

@@ -1,5 +1,13 @@
 # Omniledger 架构与开发记忆 (Memory)
 
+## 新增持仓明细的已清仓资产显示开关（基于 1e-8 精度容差过滤），并实装注入 UTF-8 BOM 的客户端 CSV 导出功能 (Task 68)
+- 在 `src/actions/portfolio.ts` 的 `getPortfolioPositions()` 函数中新增 `includeCleared: boolean = false` 参数，将清仓判定从 `quantity === 0` 升级为 `Big.js` 的 `1e-8` 精度容差过滤（`holding.quantity.gt('1e-8')`），杜绝浮点数灰尘资产被错误保留或隐藏。
+- 当 `!includeCleared` 时，自动过滤掉持仓量 ≤ 1e-8 的已清仓资产；当 `includeCleared` 为 true 时，已清仓资产会被返回，其 `marketValue` 和 `floatingPnl` 为 0，但**保留真实计算出的 `accumulatedPnl`（累计盈亏）字段**，确保历史盈亏数据不丢失。
+- 在 `app/dashboard/page.tsx` 的"持仓明细"卡片头部新增 Checkbox（显示"👁 显示历史持仓"）和 Button（"📥 导出 CSV"），Checkbox 切换时基于 `Big(pos.quantity).gt('1e-8')` 在前端动态过滤列表，无需额外请求。
+- 编写 `exportToCSV()` 客户端导出函数：定义中文字段表头（资产名称、代码、持仓量、成本价、现价、总市值、浮动盈亏、累计盈亏），将当前表格数据映射为 CSV 格式，**注入 `\uFEFF` UTF-8 BOM 头**并创建 Blob 触发下载，彻底解决 Excel 打开中文乱码问题。
+- 文件名格式为 `portfolio_details_YYYY-MM-DD.csv`，所有数值字段用双引号包裹防止逗号破坏 CSV 格式。
+- 同步更新 `getPortfolioSummary(includeCleared)` 和 `recordDailySnapshot()` 以传递参数。
+
 ## 修复腾讯行情接口 URL 拼接逻辑，剔除导致数据残缺的 s_ (简易版) 前缀，确保所有市场强制获取包含时间戳的全量报文 (Task 67)
 - 在 `app/api/cron/fetch-prices/route.ts` 的 `fetchStockPrice()` 函数与 `src/actions/market.ts` 的 `getTencentSymbol()` 函数中，将美股资产的前缀映射从 `'s_us'` 强制重构为 `'us'`。
 - **根因分析：** 腾讯财经 gtimg 接口使用 `s_us` 前缀时返回的是"简易版"报文（仅 ~10 个字段），缺失 Index 30 的日期时间字段；使用 `us` 前缀时返回"全量版"报文（60+ 个字段），包含完整的交易时间戳 `2026-05-01 16:00:06`。

app/dashboard/page.tsx

@@ -31,7 +31,7 @@ import { AddTransactionDialog } from '@/components/transactions/add-transaction-
 import { UpdateTransactionDialog } from '@/components/transactions/update-transaction-dialog';
 import { deleteTransaction } from '@/actions/transaction';
 import { importHistoricalPrices } from '@/actions/market';
-import { ChevronDown, ChevronUp, Plus, Edit3, Trash2, Upload } from 'lucide-react';
+import { ChevronDown, ChevronUp, Plus, Edit3, Trash2, Upload, Download, Eye } from 'lucide-react';
 import Big from 'big.js';
 
 const txTypeMap: Record<string, string> = {
@@ -55,6 +55,36 @@ function formatNative(value: string, baseCurrency: string): string {
   return `${symbol}${formatted}`;
 }
 
+function exportToCSV(positions: any[]) {
+  const headers = ["资产名称", "代码", "持仓量", "成本价", "现价", "总市值", "浮动盈亏", "累计盈亏"];
+
+  const rows = positions.map(item => [
+    item.name || item.symbol,
+    item.symbol,
+    item.quantity || '0',
+    new Big(item.avgCostNative || '0').toFixed(2),
+    item.latestPrice || '0',
+    new Big(item.marketValueNative || '0').toFixed(2),
+    new Big(item.floatingPnlNative || '0').toFixed(2),
+    new Big(item.cumulativePnlNative || '0').toFixed(2),
+  ]);
+
+  const csvContent = [
+    headers.join(","),
+    ...rows.map(e => e.map(val => `"${val}"`).join(","))
+  ].join("\n");
+
+  const blob = new Blob(["\uFEFF" + csvContent], { type: 'text/csv;charset=utf-8;' });
+  const url = URL.createObjectURL(blob);
+  const link = document.createElement("a");
+  link.setAttribute("href", url);
+  link.setAttribute("download", `portfolio_details_${new Date().toISOString().split('T')[0]}.csv`);
+  document.body.appendChild(link);
+  link.click();
+  document.body.removeChild(link);
+  URL.revokeObjectURL(url);
+}
+
 function formatPnl(value: string, percent: string, baseCurrency: string): { text: string; className: string } {
   const isPositive = new Big(value).gte(0);
   const symbol = getCurrencySymbol(baseCurrency);
@@ -91,11 +121,21 @@ export default function DashboardPage() {
   const [importDialogOpen, setImportDialogOpen] = useState(false);
   const [importAssetId, setImportAssetId] = useState<string>('');
   const [importText, setImportText] = useState('');
+  const [showCleared, setShowCleared] = useState(false);
+  const [positionsRaw, setPositionsRaw] = useState<any[]>([]);
+
+  useEffect(() => {
+    const filtered = showCleared
+      ? positionsRaw
+      : positionsRaw.filter(pos => new Big(pos.quantity || '0').gt('1e-8'));
+    setPositions(filtered);
+  }, [showCleared, positionsRaw]);
 
   useEffect(() => {
     async function loadData() {
-      const summary = await getPortfolioSummary();
+      const summary = await getPortfolioSummary(true);
       const allAssets = await getAssets();
+      setPositionsRaw(summary.positions);
       setPositions(summary.positions);
       setTotalCnyValue(summary.totalCnyValue);
       setTotalPnlCny(summary.totalPnlCny);
@@ -271,8 +311,29 @@ export default function DashboardPage() {
       </Card>
 
       <Card>
-        <CardHeader>
+        <CardHeader className="flex flex-row items-center justify-between space-y-0">
           <CardTitle>持仓明细</CardTitle>
+          <div className="flex items-center gap-3">
+            <label className="flex items-center gap-2 cursor-pointer text-sm text-muted-foreground hover:text-foreground transition-colors">
+              <input
+                type="checkbox"
+                checked={showCleared}
+                onChange={(e) => setShowCleared(e.target.checked)}
+                className="h-4 w-4 rounded border-border text-primary focus:ring-primary cursor-pointer"
+              />
+              <Eye className="h-4 w-4" />
+              显示历史持仓
+            </label>
+            <Button
+              size="sm"
+              variant="outline"
+              onClick={() => exportToCSV(positions)}
+              disabled={positions.length === 0}
+            >
+              <Download className="h-4 w-4 mr-1" />
+              导出 CSV
+            </Button>
+          </div>
         </CardHeader>
         <CardContent>
           {positions.length === 0 ? (

src/actions/portfolio.ts

@@ -173,7 +173,7 @@ function getTodayInShanghai(): Date {
   return new Date(utcDate.getTime() + shanghaiOffset);
 }
 
-export async function getPortfolioPositions(): Promise<Position[]> {
+export async function getPortfolioPositions(includeCleared: boolean = false): Promise<Position[]> {
   const allTransactions = await db
     .select({
       id: transactions.id,
@@ -334,11 +334,17 @@ export async function getPortfolioPositions(): Promise<Position[]> {
   const today = getTodayInShanghai();
   const result: Position[] = [];
 
+  const CLEARED_QUANTITY_TOLERANCE = new Big('1e-8');
+
   for (const [_, holding] of holdings) {
-    if (holding.quantity.lte(0)) continue;
+    const hasPosition = holding.quantity.gt(CLEARED_QUANTITY_TOLERANCE);
+
+    if (!hasPosition && !includeCleared) {
+      continue;
+    }
 
     const cnyValue = calculateCnyValueFromPrice(
-      holding.quantity,
+      hasPosition ? holding.quantity : new Big('0'),
       holding.latestPrice,
       holding.baseCurrency,
       rateMap
@@ -442,8 +448,8 @@ export async function getPortfolioPositions(): Promise<Position[]> {
   return result;
 }
 
-export async function getPortfolioSummary() {
+export async function getPortfolioSummary(includeCleared: boolean = false) {
-  const positions = await getPortfolioPositions();
+  const positions = await getPortfolioPositions(includeCleared);
 
   // 单一事实来源：复用 getPortfolioPositions 已汇率折算的结果
   let totalCnyValue = new Big('0');

src/actions/snapshots.ts

@@ -24,7 +24,7 @@ function getTodayInShanghai(): string {
 }
 
 export async function recordDailySnapshot() {
-  const positions = await getPortfolioPositions();
+  const positions = await getPortfolioPositions(false);
 
   // 统一使用 engine 输出的 marketValueCny / accumulatedPnlCny
   const totalValueCny = positions.reduce(