feat(sse): sync temps réel multi-appareils via Server-Sent Events v0.5.8

- Broadcaster asyncio.Queue avec keepalive 25s (prévient timeout proxy)
- Endpoint GET /api/events/stream (StreamingResponse text/event-stream)
- Broadcast notes_changed / todos_changed / shopping_changed sur toutes mutations
- Hook useServerEvents: EventSource avec reconnexion automatique (3s)
- Pages Notes, Todos, Shopping abonnées aux événements SSE
- nginx: location SSE dédiée (proxy_buffering off, timeout 24h)

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

backend/app/main.py

@@ -4,6 +4,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.staticfiles import StaticFiles
 from app.api.admin import router as admin_router
+from app.api.events import router as events_router
 from app.api.health import router as health_router
 from app.api.media import router as media_router
 from app.api.notes import router as notes_router
@@ -36,6 +37,7 @@ app.add_middleware(
 )
 
 app.include_router(health_router, prefix="/api")
+app.include_router(events_router, prefix="/api/events")
 app.include_router(admin_router, prefix="/api/admin")
 app.include_router(media_router, prefix="/api/media")
 app.include_router(notes_router, prefix="/api/notes")