🥅(backend) catch request timeout and Brevo contact addition errors

Handle unhandled exceptions to prevent UX impact. Marketing email operations
are optional and should not disrupt core functionality.

My first implementation was imperfect, raising error in sentry.

src/backend/core/tests/services/test_marketing.py

@@ -11,6 +11,7 @@ from django.core.exceptions import ImproperlyConfigured
 
 import brevo_python
 import pytest
+import requests
 
 from core.services.marketing import (
     BrevoMarketingService,
@@ -133,6 +134,30 @@ def test_create_contact_api_error(mock_contact_api):
         brevo_service.create_contact(valid_contact_data)
 
 
+@mock.patch("brevo_python.ContactsApi")
+def test_create_contact_timeout_error(mock_contact_api):
+    """Test contact creation timeout error handling."""
+
+    mock_api = mock_contact_api.return_value
+    settings.BREVO_API_KEY = "test-api-key"
+    settings.BREVO_API_CONTACT_LIST_IDS = [1, 2, 3, 4]
+    settings.BREVO_API_CONTACT_ATTRIBUTES = {"source": "test"}
+
+    valid_contact_data = ContactData(
+        email="test@example.com",
+        attributes={"first_name": "Test"},
+        list_ids=[1, 2],
+        update_enabled=True,
+    )
+
+    brevo_service = BrevoMarketingService()
+
+    mock_api.create_contact.side_effect = requests.exceptions.ReadTimeout()
+
+    with pytest.raises(ContactCreationError, match="Failed to create contact in Brevo"):
+        brevo_service.create_contact(valid_contact_data)
+
+
 @pytest.fixture
 def clear_marketing_cache():
     """Clear marketing service cache between tests."""