feat: add Exercise model and CRUD API for tutorial exercises

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

tutorial/urls/admin.py

@@ -1,10 +1,8 @@
 from django.urls import path
-from ..views.admin import TutorialAdminAPI, TutorialVisibilityAPI
+from ..views.admin import TutorialAdminAPI, TutorialVisibilityAPI, ExerciseAdminAPI
 
 urlpatterns = [
     path("tutorial", TutorialAdminAPI.as_view()),
-    path(
-        "tutorial/visibility",
-        TutorialVisibilityAPI.as_view(),
-    ),
+    path("tutorial/visibility", TutorialVisibilityAPI.as_view()),
+    path("exercise", ExerciseAdminAPI.as_view()),
 ]

tutorial/urls/tutorial.py

@@ -1,7 +1,8 @@
 from django.urls import path
-from ..views.oj import TutorialAPI, TutorialTitlesAPI
+from ..views.oj import TutorialAPI, TutorialTitlesAPI, ExerciseAPI
 
 urlpatterns = [
     path("tutorial", TutorialAPI.as_view()),
     path("tutorials", TutorialTitlesAPI.as_view()),
+    path("exercises", ExerciseAPI.as_view()),
 ]