feat: add Reports page and detail view to frontend

- Reports list page with type filter (daily/weekly)
- Report detail page with all sections: P&L, recommendation accuracy,
  position performance table, risk metrics, model quality windows
- Executive summary card, validation warnings display
- Nav item under Trading group
- Routes: /reports and /reports/:id

frontend/src/components/AppLayout.tsx

@@ -19,6 +19,7 @@ import {
   Globe,
   BarChart3,
   Bot,
+  ClipboardList,
 } from 'lucide-react';
 
 interface NavItem {
@@ -40,6 +41,7 @@ const navItems: NavItem[] = [
   { to: '/positions', label: 'Positions', icon: <Wallet size={18} />, group: 'Trading' },
   { to: '/trading', label: 'Trading Controls', icon: <ShieldCheck size={18} />, group: 'Trading' },
   { to: '/trading/engine', label: 'Trading Engine', icon: <BarChart3 size={18} />, group: 'Trading' },
+  { to: '/reports', label: 'Reports', icon: <ClipboardList size={18} />, group: 'Trading' },
   { to: '/ops/pipeline', label: 'Pipeline', icon: <Activity size={18} />, group: 'Ops' },
   { to: '/ops/ingestion', label: 'Ingestion', icon: <Download size={18} />, group: 'Ops' },
   { to: '/ops/model', label: 'Model Perf', icon: <Cpu size={18} />, group: 'Ops' },