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/services/__init__.py

@@ -0,0 +1,28 @@
+# app/modules/customers/services/__init__.py
+"""
+Customers module services.
+
+Re-exports customer-related services from their source locations.
+"""
+
+from app.services.customer_service import (
+    customer_service,
+    CustomerService,
+)
+from app.services.admin_customer_service import (
+    admin_customer_service,
+    AdminCustomerService,
+)
+from app.services.customer_address_service import (
+    customer_address_service,
+    CustomerAddressService,
+)
+
+__all__ = [
+    "customer_service",
+    "CustomerService",
+    "admin_customer_service",
+    "AdminCustomerService",
+    "customer_address_service",
+    "CustomerAddressService",
+]