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/definition.py

@@ -0,0 +1,68 @@
+# app/modules/orders/definition.py
+"""
+Orders module definition.
+
+Defines the orders module including its features, menu items,
+and route configurations.
+"""
+
+from app.modules.base import ModuleDefinition
+from models.database.admin_menu_config import FrontendType
+
+
+def _get_admin_router():
+    """Lazy import of admin router to avoid circular imports."""
+    from app.modules.orders.routes.admin import admin_router
+
+    return admin_router
+
+
+def _get_vendor_router():
+    """Lazy import of vendor router to avoid circular imports."""
+    from app.modules.orders.routes.vendor import vendor_router
+
+    return vendor_router
+
+
+# Orders module definition
+orders_module = ModuleDefinition(
+    code="orders",
+    name="Order Management",
+    description=(
+        "Order processing, fulfillment tracking, order item exceptions, "
+        "and bulk order operations."
+    ),
+    features=[
+        "order_management",  # Basic order CRUD
+        "order_bulk_actions",  # Bulk status updates
+        "order_export",  # Export orders to CSV/Excel
+        "automation_rules",  # Order automation rules
+        "fulfillment_tracking",  # Shipping and tracking
+        "shipping_management",  # Carrier integration
+        "order_exceptions",  # Order item exception handling
+    ],
+    menu_items={
+        FrontendType.ADMIN: [
+            "orders",  # Platform-wide order management
+        ],
+        FrontendType.VENDOR: [
+            "orders",  # Vendor order management
+        ],
+    },
+    is_core=False,
+)
+
+
+def get_orders_module_with_routers() -> ModuleDefinition:
+    """
+    Get orders module with routers attached.
+
+    This function attaches the routers lazily to avoid circular imports
+    during module initialization.
+    """
+    orders_module.admin_router = _get_admin_router()
+    orders_module.vendor_router = _get_vendor_router()
+    return orders_module
+
+
+__all__ = ["orders_module", "get_orders_module_with_routers"]