feat: AI Desks — configurable agent system for news/technical/eco processing

- New ai_desks table with CRUD (get_all/by_type/upsert/delete)
- ai_desks router: REST API + GET /signal-catalog (7 extensible signals)
- News Desk: semantic dedup via AI (±N days window, system_prompt hint)
- Technical Desk: 4 signal detectors driven by desk config
  (ma_cross, rsi_extreme, bb_squeeze, new_52w_extreme)
- 3 more signals in catalog ready to enable: price_gap, volume_spike, macd_crossover
- market_event_detector.py loads desk configs at runtime, falls back to legacy params
- AIDesks.tsx: full editor UI with signal toggles, param sliders, instrument multi-select
- Sidebar: Bot icon + /ai-desks route

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
+  History, Calendar, TrendingUp, Zap, DollarSign, Settings, BrainCircuit, Activity, BookOpen, FileBarChart, Brain, ShieldAlert, Microscope, ScrollText, Gauge, GitCompare, Building2, Users, ScanEye, CandlestickChart, PlayCircle, Radio, Bot
 } from 'lucide-react'
 import { useGeoRiskScore, useAiStatus, usePortfolioSummary } from '../../hooks/useApi'
 import clsx from 'clsx'
@@ -29,6 +29,7 @@ const nav = [
   { to: '/specialist-desks', icon: Users, label: 'Specialist Desks' },
   { to: '/instruments', icon: CandlestickChart, label: 'Instrument Analysis' },
   { to: '/market-events', icon: Radio, label: 'Market Events' },
+  { to: '/ai-desks', icon: Bot, label: 'AI Desks' },
   { to: '/cycle-actions', icon: PlayCircle, label: 'Cycle Actions' },
   { to: '/snapshot', icon: ScanEye, label: 'Snapshot Externe' },
   { to: '/logs', icon: ScrollText, label: 'System Logs' },