更新登录逻辑，等待数据库进一步完善

main/views.py

@@ -6,7 +6,7 @@ from django.views.decorators.http import require_http_methods
 def home(request):
     # Enforce login: require session user_id
     session_user_id = request.session.get("user_id")
-    if not session_user_id:
+    if session_user_id is None:
         return redirect("/accounts/login/")
 
     # Show user_id (prefer query param if present, but don't trust it)