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/schemas/__init__.py

@@ -0,0 +1,28 @@
+# app/modules/customers/schemas/__init__.py
+"""
+Customers module Pydantic schemas.
+
+Re-exports customer-related schemas from their source locations.
+"""
+
+from models.schema.customer import (
+    CustomerRegister,
+    CustomerUpdate,
+    CustomerLogin,
+    CustomerResponse,
+    CustomerListResponse,
+    CustomerAddressCreate,
+    CustomerAddressUpdate,
+    CustomerAddressResponse,
+)
+
+__all__ = [
+    "CustomerRegister",
+    "CustomerUpdate",
+    "CustomerLogin",
+    "CustomerResponse",
+    "CustomerListResponse",
+    "CustomerAddressCreate",
+    "CustomerAddressUpdate",
+    "CustomerAddressResponse",
+]