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/services/customer_service.py

@@ -431,26 +431,6 @@ class CustomerService:
 
         return customer
 
-    def update_customer_stats(
-        self, db: Session, customer_id: int, order_total: float
-    ) -> None:
-        """
-        Update customer statistics after order.
-
-        Args:
-            db: Database session
-            customer_id: Customer ID
-            order_total: Order total amount
-        """
-        customer = db.query(Customer).filter(Customer.id == customer_id).first()
-
-        if customer:
-            customer.total_orders += 1
-            customer.total_spent += order_total
-            customer.last_order_date = datetime.utcnow()
-
-            logger.debug(f"Updated stats for customer {customer.email}")
-
     def _generate_customer_number(
         self, db: Session, store_id: int, store_code: str
     ) -> str: