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/api/deps.py

@@ -620,9 +620,9 @@ def require_menu_access(menu_item_id: str, frontend_type: "FrontendType"):
             )
 
             if user_context.is_super_admin:
-                # Super admin: check user-level config
-                platform_id = None
-                user_id = user_context.id
+                # Super admin: use platform from token if selected, else global (no filtering)
+                platform_id = user_context.token_platform_id
+                user_id = None
             else:
                 # Platform admin: need platform context
                 # Try to get from request state