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/tenancy/static/store/js/settings.js

@@ -39,7 +39,6 @@ function storeSettings() {
             { id: 'invoices', label: 'Invoices', icon: 'document-text' },
             { id: 'branding', label: 'Branding', icon: 'color-swatch' },
             { id: 'domains', label: 'Domains', icon: 'globe-alt' },
-            { id: 'api', label: 'API & Payments', icon: 'key' },
             { id: 'notifications', label: 'Notifications', icon: 'bell' },
             { id: 'email', label: 'Email', icon: 'mail' }
         ],