feat: eco desk enhanced config + EUR/USD causal simulator

Eco desk (market_event_detector.py + AIDesks.tsx):
- Add currencies filter (USD via FRED, EUR/GBP/JPY/etc via ff_calendar)
- Add min_impact filter (high / high+medium / all levels)
- Add create_market_event toggle — detect surprises without creating events
- Add lookback_releases — inject last N historical releases into event description
- New _check_ff_calendar_surprises() for non-USD surprising releases
- Frontend EcoConfig: currency chips, impact dropdown, releases input, toggle

EUR/USD Simulator (EuroSimulator.tsx):
- Pure frontend causal model — no API calls, no historical data
- 3-column layout: controls | causal chain SVG | results
- FED/BCE rate sliders + hawkish/dovish tone selector
- CPI/NFP/PMI surprise inputs
- SVG causal chain: CPI→CB→2Y→ΔRate→EURUSD with dynamic colors
- Real-time pip decomposition by factor, sensitivity bars
- Route /simulator + sidebar entry

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, Gauge, GitCompare, Building2, Users, ScanEye, CandlestickChart, PlayCircle, Radio, Bot
+  History, Calendar, TrendingUp, Zap, DollarSign, Settings, BrainCircuit, Activity, BookOpen, FileBarChart, Brain, ShieldAlert, Microscope, ScrollText, Gauge, GitCompare, Building2, Users, ScanEye, CandlestickChart, PlayCircle, Radio, Bot, Sliders
 } from 'lucide-react'
 import { useGeoRiskScore, useAiStatus, usePortfolioSummary } from '../../hooks/useApi'
 import clsx from 'clsx'
@@ -25,6 +25,7 @@ const nav = [
   { to: '/position-history', icon: GitCompare, label: 'Position History' },
   { to: '/backtest', icon: History, label: 'Backtest' },
   { to: '/calendar', icon: Calendar, label: 'Calendar' },
+  { to: '/simulator', icon: Sliders, label: 'EUR/USD Simulator' },
   { to: '/macro-series', icon: TrendingUp, label: 'Macro Series' },
   { to: '/institutional', icon: Building2, label: 'Inst. Reports' },
   { to: '/specialist-desks', icon: Users, label: 'Specialist Desks' },