fix: update test fixtures for VendorTheme and CustomerPreferences schemas

- Update VendorTheme fixture to use new colors dict structure
- Update theme tests to check colors dict instead of individual fields
- Update CustomerPreferencesUpdate test for preferred_language field

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/unit/models/schema/test_customer.py

@@ -159,6 +159,7 @@ class TestCustomerResponseSchema:
             "phone": None,
             "customer_number": "CUST001",
             "marketing_consent": False,
+            "preferred_language": "fr",
             "last_order_date": None,
             "total_orders": 5,
             "total_spent": Decimal("500.00"),
@@ -339,12 +340,12 @@ class TestCustomerPreferencesUpdateSchema:
         """Test partial update with only some fields."""
         update = CustomerPreferencesUpdate(marketing_consent=True)
         assert update.marketing_consent is True
-        assert update.language is None
+        assert update.preferred_language is None
 
     def test_language_update(self):
         """Test language preference update."""
-        update = CustomerPreferencesUpdate(language="fr")
-        assert update.language == "fr"
+        update = CustomerPreferencesUpdate(preferred_language="fr")
+        assert update.preferred_language == "fr"
 
     def test_currency_update(self):
         """Test currency preference update."""