refactor: migrate products and vendor_products to module auto-discovery

- Move admin/products.py to marketplace module as admin_products.py
  (marketplace product catalog browsing)
- Move admin/vendor_products.py to catalog module as admin.py
  (vendor catalog management)
- Move vendor/products.py to catalog module as vendor.py
  (vendor's own product catalog)
- Update marketplace admin router to include products routes
- Update catalog module routes/api/__init__.py with lazy imports
- Remove legacy imports from admin and vendor API init files

All product routes now auto-discovered via module system.

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

app/api/v1/admin/__init__.py

@@ -29,7 +29,8 @@ Self-contained modules (auto-discovered from app/modules/{module}/routes/api/adm
 - billing: Subscription tiers, vendor billing, invoices
 - inventory: Stock management, inventory tracking
 - orders: Order management, fulfillment, exceptions
-- marketplace: Letzshop integration, product sync
+- marketplace: Letzshop integration, product sync, marketplace products
+- catalog: Vendor product catalog management
 - cms: Content pages management
 - customers: Customer management
 """
@@ -58,13 +59,11 @@ from . import (
     notifications,
     platform_health,
     platforms,
-    products,
     settings,
     subscriptions,  # Legacy - will be replaced by billing module router
     tests,
     users,
     vendor_domains,
-    vendor_products,
     vendor_themes,
     vendors,
 )
@@ -129,17 +128,6 @@ router.include_router(admin_users.router, tags=["admin-admin-users"])
 router.include_router(dashboard.router, tags=["admin-dashboard"])
 
 
-# ============================================================================
-# Vendor Operations (Product Catalog)
-# ============================================================================
-
-# Include marketplace product catalog management endpoints
-router.include_router(products.router, tags=["admin-marketplace-products"])
-
-# Include vendor product catalog management endpoints
-router.include_router(vendor_products.router, tags=["admin-vendor-products"])
-
-
 # ============================================================================
 # Platform Administration
 # ============================================================================