feat: add AST_CHECK_FAILED status, is_accepted helper, ast_rules field

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

problem/migrations/0010_problem_ast_rules.py

@@ -0,0 +1,18 @@
+# Generated by Django 6.0.4 on 2026-05-26 02:36
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('problem', '0009_alter_problem_accepted_number_and_more'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='problem',
+            name='ast_rules',
+            field=models.JSONField(blank=True, default=None, null=True),
+        ),
+    ]