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>

docs/deployment/launch-readiness.md

@@ -54,6 +54,7 @@ The OMS is nearly production ready with core order processing, invoicing, invent
 | Customer profile | Complete | Full profile management |
 | Customer addresses | Complete | Multiple addresses, address book |
 | Customer messages | Complete | Conversation-based messaging |
+| Currency locale | Complete | Configurable platform/vendor locale |
 
 ### Vendor Dashboard (90% Complete)
 
@@ -123,6 +124,18 @@ The OMS is nearly production ready with core order processing, invoicing, invent
 - Integration tests for shop addresses API
 - All validation scripts fixed and passing
 
+### Configurable Currency Locale
+- **Two-tier settings architecture**: Platform defaults with vendor overrides
+- **Resolution chain**: Vendor setting → AdminSetting → Environment → Hardcoded fallback
+- **Platform settings service**: New `PlatformSettingsService` for setting resolution
+- **Configuration options**:
+  - Environment: `DEFAULT_STOREFRONT_LOCALE`, `DEFAULT_CURRENCY` in `.env`
+  - Admin: `default_storefront_locale`, `default_currency` in AdminSetting table
+  - Vendor: `storefront_locale` field on Vendor model (nullable = inherit)
+- **Supported locales**: fr-LU, de-DE, de-LU, en-GB, nl-BE, etc.
+- **Frontend**: `window.SHOP_CONFIG` provides locale/currency to JavaScript
+- **Shared formatPrice()**: Single implementation in `shop-layout.js`
+
 ---
 
 ## Remaining Gaps