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/App.tsx

@@ -27,6 +27,7 @@ import ExternalSnapshot from './pages/ExternalSnapshot'
 import InstrumentDashboard from './pages/InstrumentDashboard'
 import CycleActions from './pages/CycleActions'
 import MarketEvents from './pages/MarketEvents'
+import AIDesks from './pages/AIDesks'
 import { Navigate } from 'react-router-dom'
 import { useCycleWatcher } from './hooks/useApi'
 
@@ -74,6 +75,7 @@ export default function App() {
             <Route path="/timeline" element={<Navigate to="/market-events" replace />} />
             <Route path="/market-events" element={<MarketEvents />} />
             <Route path="/cycle-actions" element={<CycleActions />} />
+            <Route path="/ai-desks" element={<AIDesks />} />
           </Routes>
         </main>
       </div>