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/orders/schemas/__init__.py

@@ -0,0 +1,36 @@
+# app/modules/orders/schemas/__init__.py
+"""
+Orders module Pydantic schemas.
+
+Re-exports order-related schemas from their source locations.
+"""
+
+from models.schema.order import (
+    OrderCreate,
+    OrderItemCreate,
+    OrderResponse,
+    OrderItemResponse,
+    OrderListResponse,
+    AddressSnapshot,
+    CustomerSnapshot,
+)
+from models.schema.invoice import (
+    InvoiceResponse,
+    InvoiceSettingsCreate,
+    InvoiceSettingsUpdate,
+    InvoiceSettingsResponse,
+)
+
+__all__ = [
+    "OrderCreate",
+    "OrderItemCreate",
+    "OrderResponse",
+    "OrderItemResponse",
+    "OrderListResponse",
+    "AddressSnapshot",
+    "CustomerSnapshot",
+    "InvoiceResponse",
+    "InvoiceSettingsCreate",
+    "InvoiceSettingsUpdate",
+    "InvoiceSettingsResponse",
+]