feat(reaction): 用户端表情接口

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

oj/urls.py

@@ -15,6 +15,7 @@ urlpatterns = [
     path("api/admin/", include("submission.urls.admin")),
     path("api/admin/", include("utils.urls")),
     path("api/", include("message.urls.oj")),
+    path("api/", include("reaction.urls.oj")),
     path("api/", include("comment.urls.oj")),
     path("api/admin/", include("comment.urls.admin")),
     path("api/", include("tutorial.urls.tutorial")),