feat: page VaR Analyse avec approche delta Black-Scholes

- Service var_service.py : calcul VaR Historique / Paramétrique / Monte Carlo
  stressé (vol ×1.5) + CVaR par méthode, deltas BS par position, fallback
  synthétique si yfinance indisponible
- Router /api/var/compute : paramètres confidence, horizon, lookback, IV défaut
- Page VaRAnalysis.tsx : cartes métriques %, montants EUR, histogramme retours,
  VaR glissante 30j, tableau positions + deltas, backtest Kupiec pass/fail
- Route /var + nav sidebar « VaR Analyse »

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -1,7 +1,7 @@
 import { NavLink } from 'react-router-dom'
 import {
   LayoutDashboard, Globe, BarChart2, FlaskConical,
-  History, Calendar, TrendingUp, Zap, DollarSign, Settings, BrainCircuit, Activity, BookOpen, FileBarChart, Brain, ShieldAlert, Microscope, ScrollText
+  History, Calendar, TrendingUp, Zap, DollarSign, Settings, BrainCircuit, Activity, BookOpen, FileBarChart, Brain, ShieldAlert, Microscope, ScrollText, Gauge
 } from 'lucide-react'
 import { useGeoRiskScore, useAiStatus, usePortfolioSummary } from '../../hooks/useApi'
 import clsx from 'clsx'
@@ -20,6 +20,7 @@ const nav = [
   { to: '/analytics', icon: FlaskConical, label: 'Analytics' },
   { to: '/analytics-advanced', icon: Microscope, label: 'Analytics Avancées' },
   { to: '/risk', icon: ShieldAlert, label: 'Risk Dashboard' },
+  { to: '/var', icon: Gauge, label: 'VaR Analyse' },
   { to: '/backtest', icon: History, label: 'Backtest' },
   { to: '/calendar', icon: Calendar, label: 'Calendrier' },
   { to: '/logs', icon: ScrollText, label: 'Logs Système' },