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/modules/orders/routes/admin.py

@@ -0,0 +1,40 @@
+# app/modules/orders/routes/admin.py
+"""
+Orders module admin routes.
+
+This module wraps the existing admin orders routes and adds
+module-based access control. Routes are re-exported from the
+original location with the module access dependency.
+
+Includes:
+- /orders/* - Order management
+- /order-item-exceptions/* - Exception handling
+"""
+
+from fastapi import APIRouter, Depends
+
+from app.api.deps import require_module_access
+
+# Import original routers
+from app.api.v1.admin import orders as orders_routes
+from app.api.v1.admin import order_item_exceptions as exceptions_routes
+
+# Create module-aware router for orders
+admin_router = APIRouter(
+    prefix="/orders",
+    dependencies=[Depends(require_module_access("orders"))],
+)
+
+# Re-export all routes from the original orders module
+for route in orders_routes.router.routes:
+    admin_router.routes.append(route)
+
+# Create separate router for order item exceptions
+# This is included separately in the admin __init__.py
+admin_exceptions_router = APIRouter(
+    prefix="/order-item-exceptions",
+    dependencies=[Depends(require_module_access("orders"))],
+)
+
+for route in exceptions_routes.router.routes:
+    admin_exceptions_router.routes.append(route)