feat: add self-contained structure to remaining modules

Add exceptions, models, schemas, services directories to modules:

customers:
- exceptions.py, models/, schemas/, services/

inventory:
- exceptions.py, models/, schemas/, services/

messaging:
- exceptions.py, models/, schemas/, services/

monitoring:
- exceptions.py, models/, schemas/, services/

orders:
- exceptions.py, models/, schemas/, services/

payments:
- Updated __init__.py

All modules now have the standard self-contained directory
structure ready for future migration of business logic.

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

app/modules/customers/__init__.py

@@ -2,21 +2,34 @@
 """
 Customers Module - Customer database and management.
 
-This module provides:
+This is a self-contained core module providing:
+- Customer registration and authentication
 - Customer profiles and contact information
+- Customer address management
 - Customer segmentation and tags
-- Purchase history tracking
-- Customer exports
 
-Routes:
-- Admin: /api/v1/admin/customers/*
-- Vendor: /api/v1/vendor/customers/*
-
-Menu Items:
-- Admin: customers
-- Vendor: customers
+Module Structure:
+- models/ - Database models (Customer, CustomerAddress, etc.)
+- services/ - Business logic (CustomerService, CustomerAddressService)
+- schemas/ - Pydantic DTOs
+- routes/ - API routes
+- exceptions.py - Module-specific exceptions
 """
 
-from app.modules.customers.definition import customers_module
+# Use lazy imports to avoid circular import issues
 
-__all__ = ["customers_module"]
+
+def __getattr__(name: str):
+    """Lazy import module components to avoid circular imports."""
+    if name == "customers_module":
+        from app.modules.customers.definition import customers_module
+
+        return customers_module
+    elif name == "get_customers_module_with_routers":
+        from app.modules.customers.definition import get_customers_module_with_routers
+
+        return get_customers_module_with_routers
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
+
+
+__all__ = ["customers_module", "get_customers_module_with_routers"]