Lesson.figures: fixed diagrams per lesson (stored once, served with the lesson); gen_lesson_figures; 3 calculus-12 lessons

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

content/tests_lesson_figures.py

@@ -0,0 +1,17 @@
+from django.test import TestCase
+from rest_framework.test import APIClient
+
+from content.models import Grade, Lesson, Node, Unit
+
+
+class LessonFiguresTests(TestCase):
+    def test_intro_returns_stored_figures_and_empty_list_by_default(self):
+        grade = Grade.objects.create(title='دوازدهم', number=12)
+        unit = Unit.objects.create(grade=grade, title='u', order=1)
+        node = Node.objects.create(unit=unit, title='n', order=1)
+        fig = {'where': 'step', 'index': 0, 'diagram': {'kind': 'plane', 'title': 't'}}
+        with_fig = Lesson.objects.create(node=node, title='a', intro_text='x', steps=['s'], figures=[fig])
+        plain = Lesson.objects.create(node=node, title='b', intro_text='x')
+        c = APIClient()
+        self.assertEqual(c.get(f'/api/lessons/{with_fig.id}/intro').json()['figures'], [fig])
+        self.assertEqual(c.get(f'/api/lessons/{plain.id}/intro').json()['figures'], [])