feat(web): M8.6b 回测页做实 + 首页入口更新（零新后端 API）

- backtest 页：成本参数表单（手续费/印花税/滑点 %）+ 初始资金 → ResearchSpec.costs/
  initial_capital；结果新增年度收益卡与成交明细表（买/卖日、买/卖价、收益、累计换手）
- Dashboard 入口卡加入「股票筛选」「交易信号」（6 张）
- lib/types.ts：ResearchSpec 增加 price_adjustment/costs/portfolio/initial_capital，
  Trade 补 entry_price/exit_price
- 页面 200 冒烟 + tsc --noEmit 通过

frontend/web/lib/types.ts

@@ -27,9 +27,18 @@ export interface ResearchSpec {
     min_listing_days?: number;
     symbols?: string[];
   };
+  price_adjustment?: "none" | "qfq";
   factors: { name: string; weight: number }[];
   selection: { top_n: number };
   rebalance: "weekly" | "monthly";
+  costs?: {
+    commission_rate?: number;
+    stamp_tax_rate?: number;
+    slippage_rate?: number;
+    benchmark?: string;
+  };
+  portfolio?: { weighting?: string; max_position_pct?: number | null; max_industry_weight_pct?: number | null };
+  initial_capital?: number;
   period: [string, string];
 }
 
@@ -60,7 +69,7 @@ export interface BacktestResult {
   monthly_returns: { year: number; month: number; return_pct: number }[];
   yearly_returns: { year: number; return_pct: number }[];
   positions: { date: string; symbol: string; weight: number }[];
-  trades: { entry_date: string; exit_date: string; symbol: string; return_pct: number }[];
+  trades: { entry_date: string; exit_date: string; symbol: string; entry_price?: number; exit_price?: number; return_pct: number }[];
   turnover_pct: number;
   unimplemented: string[];
   config_snapshot: Record<string, unknown>;