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/app/page.tsx

@@ -36,6 +36,20 @@ const LINKS = [
     icon: "gauge" as const,
     tone: "quick-card--warn",
   },
+  {
+    href: "/selection",
+    title: "股票筛选",
+    desc: "因子评分 TopN 或条件选股，支持当前/历史时点，结果可解释",
+    icon: "target" as const,
+    tone: "quick-card--violet",
+  },
+  {
+    href: "/signals",
+    title: "交易信号",
+    desc: "按评分排名 + 趋势规则输出 BUY / WATCH / SELL 及理由",
+    icon: "scale" as const,
+    tone: "quick-card--pos",
+  },
   {
     href: "/stocks",
     title: "股票池",