Hoàn thành chức năng collaborative

backend/app/main.py

@@ -3,7 +3,7 @@ from contextlib import asynccontextmanager
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
-from .routers import annotations, auth, pdfs
+from .routers import annotations, auth, pdfs, ws
 
 
 @asynccontextmanager
@@ -17,7 +17,7 @@ app = FastAPI(title="LMS API", lifespan=lifespan)
 
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=["http://localhost:3000"],  # Next.js dev server
+    allow_origins=["http://localhost:3000", "http://localhost:3001"],
     allow_credentials=True,                   # required for cookies
     allow_methods=["*"],
     allow_headers=["*"],
@@ -26,3 +26,4 @@ app.add_middleware(
 app.include_router(auth.router, prefix="/api")
 app.include_router(pdfs.router, prefix="/api")
 app.include_router(annotations.router, prefix="/api")
+app.include_router(ws.router)  # WebSocket — no /api prefix (ws:// path)