added email_sent field to student model, do not send mail twice if not needed

cntmanage/flightslot/migrations/0031_student_mail_sent_alter_student_phone.py

@@ -0,0 +1,24 @@
+# Generated by Django 5.2.8 on 2025-12-10 10:28
+
+import phonenumber_field.modelfields
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('flightslot', '0030_weekpreference_inserted_alter_availability_week_and_more'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='student',
+            name='mail_sent',
+            field=models.BooleanField(default=False),
+        ),
+        migrations.AlterField(
+            model_name='student',
+            name='phone',
+            field=phonenumber_field.modelfields.PhoneNumberField(db_index=True, max_length=128, null=True, region=None, unique=True),
+        ),
+    ]