fix: update admin contact validation error code

- Change error code from 2004 to 2306 for admin contact validation
- Add explicit validation check for required admin contacts
- Update tests to expect new error code

The error code 2306 better reflects the EPP standard for policy-based
validation failures. This change makes the error handling more consistent
with EPP specifications when validating admin contact requirements.

app/models/epp/domain.rb

@@ -29,6 +29,12 @@ def validate_contacts
     active_admins = admin_domain_contacts.select { |x| !x.marked_for_destruction? }
     active_techs = tech_domain_contacts.select { |x| !x.marked_for_destruction? }
 
+    # Проверка количества админ контактов
+    if require_admin_contacts? && active_admins.empty?
+      add_epp_error('2306', 'contact', nil, 'Admin contacts are required')
+      ok = false
+    end
+
     # validate registrant here as well
     ([Contact.find(registrant.id)] + active_admins + active_techs).each do |x|
       unless x.valid?

test/integration/repp/v1/domains/contacts_test.rb

@@ -142,7 +142,7 @@ def test_can_not_remove_one_and_only_contact
 
     @domain.reload
     assert_response :bad_request
-    assert_equal 2004, json[:code]
+    assert_equal 2306, json[:code]
 
     assert @domain.admin_contacts.any?
   end
@@ -159,7 +159,7 @@ def test_cannot_remove_admin_contact_for_legal_entity
     json = JSON.parse(response.body, symbolize_names: true)
 
     assert_response :bad_request
-    assert_equal 2004, json[:code]
+    assert_equal 2306, json[:code]
     assert @domain.admin_contacts.any?
   end
 
@@ -178,7 +178,7 @@ def test_cannot_remove_admin_contact_for_underage_private_registrant
     json = JSON.parse(response.body, symbolize_names: true)
 
     assert_response :bad_request
-    assert_equal 2004, json[:code]
+    assert_equal 2306, json[:code]
     assert @domain.admin_contacts.any?
   end
 
@@ -217,7 +217,7 @@ def test_cannot_remove_admin_contact_for_underage_estonian_id
     json = JSON.parse(response.body, symbolize_names: true)
 
     assert_response :bad_request
-    assert_equal 2004, json[:code]
+    assert_equal 2306, json[:code]
     assert @domain.admin_contacts.any?
   end