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/migrations/0011_lesson_figures.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.2.17 on 2026-10-07 12:45
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('content', '0010_seedrecord'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='lesson',
+            name='figures',
+            field=models.JSONField(blank=True, default=list),
+        ),
+    ]