feat(users): normalize email identity storage

apps/users/api/serializers.py

@@ -4,6 +4,7 @@ from drf_spectacular.utils import extend_schema_serializer
 from rest_framework import serializers
 
 from core.serializers.base import BaseModelSerializer
+from apps.users.email_identity import normalize_email_identity
 
 User = get_user_model()
 
@@ -186,6 +187,20 @@ class UserProfileSerializer(BaseModelSerializer):
     full_name = serializers.ReadOnlyField()
     age = serializers.ReadOnlyField()
 
+    def validate_email(self, value):
+        normalized = normalize_email_identity(value)
+        user = self.instance
+
+        if normalized is None:
+            return None
+
+        existing = User.objects.filter(email=normalized)
+        if user is not None:
+            existing = existing.exclude(pk=user.pk)
+        if existing.exists():
+            raise serializers.ValidationError("A user with this email already exists.")
+        return normalized
+
     class Meta:
         model = User
         fields = BaseModelSerializer.Meta.fields + (