feat: Impact Monitor — AI impact evaluation for eco events & geopolitical news

- New DB tables: event_categories (18 bootstrap categories) + instrument_impacts
- impact_categories_bootstrap.py: FOMC/NFP/CPI/GDP/PCE/ISM/BOJ/ECB/BOE/OPEC+ + 7 géopolitical categories with per-instrument sensitivity & direction defaults
- impact_service.py: GPT-4o-mini evaluation (0-1 score, direction, rationale) + monitor data aggregation
- routers/impact.py: GET/POST endpoints for evaluate/bulk/monitor/adjust/categories
- ImpactMonitor.tsx: two-tab page (Évalués / À évaluer), top instruments bar, inline score override modal, category browser
- Startup auto-bootstrap for impact categories
- Route /impact + sidebar nav entry

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

frontend/src/App.tsx

@@ -26,6 +26,7 @@ import SpecialistDesks from './pages/SpecialistDesks'
 import Timeline from './pages/Timeline'
 import ExternalSnapshot from './pages/ExternalSnapshot'
 import InstrumentDashboard from './pages/InstrumentDashboard'
+import ImpactMonitor from './pages/ImpactMonitor'
 import { Navigate } from 'react-router-dom'
 import { useCycleWatcher } from './hooks/useApi'
 
@@ -69,6 +70,7 @@ export default function App() {
             <Route path="/snapshot" element={<ExternalSnapshot />} />
             <Route path="/instruments" element={<Navigate to="/instruments/SPY" replace />} />
             <Route path="/instruments/:id" element={<InstrumentDashboard />} />
+            <Route path="/impact" element={<ImpactMonitor />} />
           </Routes>
         </main>
       </div>