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/vendor/__init__.py

@@ -19,6 +19,7 @@ Self-contained modules (auto-discovered from app/modules/{module}/routes/api/ven
 - inventory: Stock management, inventory tracking
 - orders: Order management, fulfillment, exceptions
 - marketplace: Letzshop integration, product sync
+- catalog: Vendor product catalog management
 - cms: Content pages management
 - customers: Customer management
 """
@@ -41,7 +42,6 @@ from . import (
     notifications,
     onboarding,
     payments,
-    products,
     profile,
     settings,
     team,
@@ -71,8 +71,7 @@ router.include_router(email_templates.router, tags=["vendor-email-templates"])
 router.include_router(email_settings.router, tags=["vendor-email-settings"])
 router.include_router(onboarding.router, tags=["vendor-onboarding"])
 
-# Business operations (with prefixes: /products/*, etc.)
-router.include_router(products.router, tags=["vendor-products"])
+# Business operations (with prefixes: /invoices/*, /team/*)
 router.include_router(invoices.router, tags=["vendor-invoices"])
 router.include_router(team.router, tags=["vendor-team"])