feat: Market Events admin page — source_refs + per-instrument impacts

- DB: colonne source_refs sur market_events (migration idempotente)
- save/update_market_event: persist source_refs (JSON array de {url,title,source})
- market_event_detector: stocke source_refs + évalue impacts instruments après chaque création
- Nouveau router /api/market-events: CRUD + evaluate + impacts CRUD
- Page MarketEvents.tsx: liste filtrée/triée + panneau détail (sources cliquables,
  tableau impacts par instrument avec score/direction/rationale inline-éditables,
  ajout manuel, bulk-evaluate)
- Sidebar: entrée Market Events (Radio icon)

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

backend/main.py

@@ -7,6 +7,7 @@ from routers import timeline as timeline_router
 from routers import instruments as instruments_router
 from routers import impact as impact_router
 from routers import cycle_actions as cycle_actions_router
+from routers import market_events as market_events_router
 from routers import logs as logs_router
 from routers import var as var_router
 from routers import reports as reports_router
@@ -141,6 +142,7 @@ app.include_router(timeline_router.router)
 app.include_router(instruments_router.router)
 app.include_router(impact_router.router)
 app.include_router(cycle_actions_router.router)
+app.include_router(market_events_router.router)
 
 
 @app.get("/")