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/static/admin/js/customers.js

@@ -27,11 +27,7 @@ function adminCustomers() {
         stats: {
             total: 0,
             active: 0,
-            inactive: 0,
-            with_orders: 0,
-            total_spent: 0,
-            total_orders: 0,
-            avg_order_value: 0
+            inactive: 0
         },
 
         // Pagination (standard structure matching pagination macro)
@@ -375,17 +371,6 @@ function adminCustomers() {
             }
         },
 
-        /**
-         * Format currency for display
-         */
-        formatCurrency(amount) {
-            if (amount == null) return '-';
-            return new Intl.NumberFormat('de-DE', {
-                style: 'currency',
-                currency: 'EUR'
-            }).format(amount);
-        },
-
         /**
          * Format date for display
          */