add problem prompt

problem/migrations/0002_problem_prompt.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.2.3 on 2025-10-03 16:31
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('problem', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='problem',
+            name='prompt',
+            field=models.TextField(null=True),
+        ),
+    ]