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>

app/routes/admin_pages.py

@@ -536,18 +536,26 @@ async def admin_marketplace_page(
     )
 
 
-@router.get("/letzshop", response_class=HTMLResponse, include_in_schema=False)
-async def admin_letzshop_page(
+# ============================================================================
+# MARKETPLACE INTEGRATION ROUTES
+# ============================================================================
+
+
+@router.get(
+    "/marketplace/letzshop", response_class=HTMLResponse, include_in_schema=False
+)
+async def admin_marketplace_letzshop_page(
     request: Request,
     current_user: User = Depends(get_current_admin_from_cookie_or_header),
     db: Session = Depends(get_db),
 ):
     """
-    Render Letzshop management page.
-    Admin overview of Letzshop integration for all vendors.
+    Render unified Letzshop management page.
+    Combines products (import/export), orders, and settings management.
+    Admin can select a vendor and manage their Letzshop integration.
     """
     return templates.TemplateResponse(
-        "admin/letzshop.html",
+        "admin/marketplace-letzshop.html",
         {
             "request": request,
             "user": current_user,