feat: multi-module improvements across merchant, store, i18n, and customer systems

- Fix platform-grouped merchant sidebar menu with core items at root level
- Add merchant store management (detail page, create store, team page)
- Fix store settings 500 error by removing dead stripe/API tab
- Move onboarding translations to module-owned locale files
- Fix onboarding banner i18n with server-side rendering + context inheritance
- Refactor login language selectors to use languageSelector() function (LANG-002)
- Move HTTPException handling to global exception handler in merchant routes (API-003)
- Add language selector to all login pages and portal headers
- Fix customer module: drop order stats from customer model, add to orders module
- Fix admin menu config visibility for super admin platform context
- Fix storefront auth and layout issues
- Add missing i18n translations for onboarding steps (en/fr/de/lb)

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

app/modules/customers/tests/unit/test_customer_schema.py

@@ -149,7 +149,6 @@ class TestCustomerResponseSchema:
     def test_from_dict(self):
         """Test creating response from dict."""
         from datetime import datetime
-        from decimal import Decimal
 
         data = {
             "id": 1,
@@ -161,9 +160,6 @@ class TestCustomerResponseSchema:
             "customer_number": "CUST001",
             "marketing_consent": False,
             "preferred_language": "fr",
-            "last_order_date": None,
-            "total_orders": 5,
-            "total_spent": Decimal("500.00"),
             "is_active": True,
             "created_at": datetime.now(),
             "updated_at": datetime.now(),
@@ -171,7 +167,7 @@ class TestCustomerResponseSchema:
         response = CustomerResponse(**data)
         assert response.id == 1
         assert response.customer_number == "CUST001"
-        assert response.total_orders == 5
+        assert response.preferred_language == "fr"
 
 
 @pytest.mark.unit