feat: add unified admin Marketplace Letzshop page

- Add new Marketplace section in admin sidebar with Letzshop sub-item
- Remove old Import and Letzshop Orders items from Product Catalog
- Create unified Letzshop management page with 3 tabs:
  - Products tab: Import/Export functionality
  - Orders tab: Order management with confirm/reject/tracking
  - Settings tab: API credentials and CSV URLs
- Add unified jobs table showing imports, exports, and order syncs
- Implement vendor autocomplete using Tom Select library (CDN + fallback)
- Add /vendors/{vendor_id}/jobs API endpoint for unified job listing
- Move database queries to service layer (LetzshopOrderService)
- Add LetzshopJobItem and LetzshopJobsListResponse schemas
- Include Tom Select CSS/JS assets as local fallback

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

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

static/admin/js/init-alpine.js

@@ -29,6 +29,7 @@ function data() {
   const defaultSections = {
     platformAdmin: true,
     productCatalog: false,
+    marketplace: false,
     contentMgmt: false,
     devTools: false,
     platformHealth: false,
@@ -66,7 +67,8 @@ function data() {
     // Product Catalog
     'marketplace-products': 'productCatalog',
     'vendor-products': 'productCatalog',
-    marketplace: 'productCatalog',
+    // Marketplace
+    'marketplace-letzshop': 'marketplace',
     // Content Management
     'platform-homepage': 'contentMgmt',
     'content-pages': 'contentMgmt',