feat: add configurable currency locale and fix vendor JS init

Currency Locale Configuration:
- Add platform-level storefront settings (locale, currency)
- Create PlatformSettingsService with resolution chain:
  vendor → AdminSetting → environment → hardcoded fallback
- Add storefront_locale nullable field to Vendor model
- Update shop routes to resolve and pass locale to templates
- Add window.SHOP_CONFIG for frontend JavaScript access
- Centralize formatPrice() in shop-layout.js using SHOP_CONFIG
- Remove local formatPrice functions from shop templates

Vendor JS Bug Fix:
- Fix vendorCode being null on all vendor pages
- Root cause: page components overriding init() without calling parent
- Add parent init call to 14 vendor JS files
- Add JS-013 architecture rule to prevent future regressions
- Validator now checks vendor JS files for parent init pattern

Files changed:
- New: app/services/platform_settings_service.py
- New: alembic/versions/s7a8b9c0d1e2_add_storefront_locale_to_vendors.py
- Modified: 14 vendor JS files, shop templates, validation scripts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/templates/shop/account/profile.html

@@ -523,13 +523,7 @@ function shopProfilePage() {
             }
         },
 
-        formatPrice(amount) {
-            if (!amount && amount !== 0) return '-';
-            return new Intl.NumberFormat('fr-LU', {
-                style: 'currency',
-                currency: 'EUR'
-            }).format(amount);
-        },
+        // formatPrice is inherited from shopLayoutData() via spread operator
 
         formatDate(dateStr) {
             if (!dateStr) return '-';