feat: extract inventory, orders, and marketplace modules (Phase 4)

Extract three additional modules following the billing module pattern:

Inventory Module (app/modules/inventory/):
- Stock management and tracking
- Inventory locations
- Low stock alerts
- Admin and vendor routes with module access control

Orders Module (app/modules/orders/):
- Order management and fulfillment
- Order item exceptions
- Bulk operations and export
- Admin and vendor routes with module access control

Marketplace Module (app/modules/marketplace/):
- Letzshop integration
- Product sync
- Marketplace import
- Depends on inventory module
- Admin and vendor routes with module access control

Admin router updated:
- Uses module routers with require_module_access dependency
- Legacy router includes commented out
- Routes verified: 15 inventory, 16 orders, 42 marketplace

All 31 module tests passing.

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

app/api/v1/admin/__init__.py

@@ -27,12 +27,15 @@ based on platform context (not at route registration time).
 
 Extracted modules (app/modules/{module}/routes/):
 - billing: Subscription tiers, vendor billing, invoices
+- inventory: Stock management, inventory tracking
+- orders: Order management, fulfillment, exceptions
+- marketplace: Letzshop integration, product sync
 
-Future extractions will follow the same pattern:
+Module extraction pattern:
 1. Create app/modules/{module}/ directory
-2. Move routes to app/modules/{module}/routes/admin.py
-3. Add require_module_access("{module}") to router
-4. Update this file to import from module instead
+2. Create routes/admin.py with require_module_access("{module}") dependency
+3. Import module router here and include it
+4. Comment out legacy router include
 """
 
 from fastapi import APIRouter
@@ -77,6 +80,11 @@ from . import (
 
 # Import extracted module routers
 from app.modules.billing.routes import admin_router as billing_admin_router
+from app.modules.inventory.routes import admin_router as inventory_admin_router
+from app.modules.orders.routes.admin import admin_router as orders_admin_router
+from app.modules.orders.routes.admin import admin_exceptions_router as orders_exceptions_router
+from app.modules.marketplace.routes.admin import admin_router as marketplace_admin_router
+from app.modules.marketplace.routes.admin import admin_letzshop_router as letzshop_admin_router
 
 # Create admin router
 router = APIRouter()
@@ -141,7 +149,7 @@ router.include_router(dashboard.router, tags=["admin-dashboard"])
 
 
 # ============================================================================
-# Vendor Operations (Product Catalog, Inventory & Orders)
+# Vendor Operations (Product Catalog, Inventory & Orders) - Module-gated
 # ============================================================================
 
 # Include marketplace product catalog management endpoints
@@ -150,27 +158,26 @@ 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"])
 
-# Include inventory management endpoints
-router.include_router(inventory.router, tags=["admin-inventory"])
+# Include inventory module router (with module access control)
+router.include_router(inventory_admin_router, tags=["admin-inventory"])
+# Legacy: router.include_router(inventory.router, tags=["admin-inventory"])
 
-# Include order management endpoints
-router.include_router(orders.router, tags=["admin-orders"])
-
-# Include order item exception management endpoints
-router.include_router(
-    order_item_exceptions.router, tags=["admin-order-exceptions"]
-)
+# Include orders module router (with module access control)
+router.include_router(orders_admin_router, tags=["admin-orders"])
+router.include_router(orders_exceptions_router, tags=["admin-order-exceptions"])
+# Legacy: router.include_router(orders.router, tags=["admin-orders"])
+# Legacy: router.include_router(order_item_exceptions.router, tags=["admin-order-exceptions"])
 
 
 # ============================================================================
-# Marketplace & Imports
+# Marketplace & Imports (Module-gated)
 # ============================================================================
 
-# Include marketplace monitoring endpoints
-router.include_router(marketplace.router, tags=["admin-marketplace"])
-
-# Include Letzshop integration endpoints
-router.include_router(letzshop.router, tags=["admin-letzshop"])
+# Include marketplace module router (with module access control)
+router.include_router(marketplace_admin_router, tags=["admin-marketplace"])
+router.include_router(letzshop_admin_router, tags=["admin-letzshop"])
+# Legacy: router.include_router(marketplace.router, tags=["admin-marketplace"])
+# Legacy: router.include_router(letzshop.router, tags=["admin-letzshop"])
 
 
 # ============================================================================