feat(accounts): home district with 6-month cooldown

- accounts/models.py: add district_changed_at DateTimeField + VALID_DISTRICTS constant (14 Kerala districts)
- migration 0013_user_district_changed_at: nullable DateTimeField, no backfill
- WebRegisterForm: accept optional district during signup, stamp district_changed_at
- UpdateProfileView: enforce 183-day cooldown with human-readable error
- LoginView/WebRegisterView/StatusView: include district_changed_at in responses

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

accounts/migrations/0013_user_district_changed_at.py

@@ -0,0 +1,16 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('accounts', '0012_user_eventify_id'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='user',
+            name='district_changed_at',
+            field=models.DateTimeField(blank=True, null=True),
+        ),
+    ]

accounts/models.py

@@ -24,6 +24,12 @@ ROLE_CHOICES = (
         ('partner_customer', 'Partner Customer'),
     )
 
+VALID_DISTRICTS = [
+    "Thiruvananthapuram", "Kollam", "Pathanamthitta", "Alappuzha", "Kottayam",
+    "Idukki", "Ernakulam", "Thrissur", "Palakkad", "Malappuram",
+    "Kozhikode", "Wayanad", "Kannur", "Kasaragod",
+]
+
 class User(AbstractUser):
     eventify_id = models.CharField(
         max_length=12,
@@ -49,6 +55,7 @@ class User(AbstractUser):
     state = models.CharField(max_length=100, blank=True, null=True)
     country = models.CharField(max_length=100, blank=True, null=True)
     place = models.CharField(max_length=200, blank=True, null=True)
+    district_changed_at = models.DateTimeField(blank=True, null=True)
 
     # Location fields
     latitude = models.DecimalField(max_digits=9, decimal_places=6, blank=True, null=True)