feat: add Exercise model and CRUD API for tutorial exercises

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

tutorial/migrations/0004_exercise.py

@@ -0,0 +1,29 @@
+# Generated by Django 6.0 on 2026-04-23 07:31
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('tutorial', '0003_alter_tutorial_code'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Exercise',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('type', models.CharField(choices=[('mcq', '选择题'), ('sort', '代码排序')], max_length=16)),
+                ('data', models.JSONField()),
+                ('order', models.IntegerField(default=0)),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('tutorial', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='exercises', to='tutorial.tutorial')),
+            ],
+            options={
+                'db_table': 'exercise',
+                'ordering': ['order', 'created_at'],
+            },
+        ),
+    ]