add created_at field to state model

services/backend/apps/competition/migrations/0004_state_changed_at.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.1.6 on 2025-03-01 08:10
+
+import datetime
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('competition', '0003_state'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='state',
+            name='changed_at',
+            field=models.DateTimeField(default=datetime.datetime.now),
+        ),
+    ]