add index for models

message/migrations/0002_message_message_recipient_time_idx.py

@@ -0,0 +1,20 @@
+# Generated by Django 6.0 on 2026-04-23 20:07
+
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('message', '0001_initial'),
+        ('submission', '0004_submission_problem_user_idx'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name='message',
+            index=models.Index(fields=['recipient', 'create_time'], name='message_recipient_time_idx'),
+        ),
+    ]