feat: add Exercise model and CRUD API for tutorial exercises

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

tutorial/views/oj.py

@@ -1,7 +1,7 @@
 from utils.api import APIView
 
-from tutorial.models import Tutorial
-from tutorial.serializers import TutorialSerializer
+from tutorial.models import Tutorial, Exercise
+from tutorial.serializers import TutorialSerializer, ExerciseSerializer
 
 
 class TutorialAPI(APIView):
@@ -21,3 +21,16 @@ class TutorialTitlesAPI(APIView):
             "id", "title"
         )
         return self.success(list(tutorials))
+
+
+class ExerciseAPI(APIView):
+    def get(self, request):
+        tutorial_id = request.GET.get("tutorial_id")
+        if not tutorial_id:
+            return self.error("tutorial_id is required")
+        try:
+            tutorial = Tutorial.objects.get(id=tutorial_id, is_public=True)
+        except Tutorial.DoesNotExist:
+            return self.error("Tutorial does not exist")
+        exercises = Exercise.objects.filter(tutorial=tutorial)
+        return self.success(ExerciseSerializer(exercises, many=True).data)