refactor(arch): use CustomerContext schema for dependency injection

Phase 5 of storefront restructure plan - fix direct model imports in
API routes by using schemas for dependency injection.

Created CustomerContext schema:
- Lightweight Pydantic model for customer data in API routes
- Populated from Customer DB model in auth dependency
- Contains all fields needed by storefront routes
- Includes from_db_model() factory method

Updated app/api/deps.py:
- _validate_customer_token now returns CustomerContext instead of Customer
- Updated docstrings for all customer auth functions

Updated module storefront routes:
- customers: Uses CustomerContext for profile/address endpoints
- orders: Uses CustomerContext for order history endpoints
- checkout: Uses CustomerContext for order placement
- messaging: Uses CustomerContext for messaging endpoints

This enforces the layered architecture (Routes → Services → Models)
by ensuring API routes never import database models directly.

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

app/modules/checkout/routes/api/storefront.py

@@ -26,10 +26,10 @@ from app.modules.checkout.schemas import (
     CheckoutSessionResponse,
 )
 from app.modules.checkout.services import checkout_service
+from app.modules.customers.schemas import CustomerContext
 from app.modules.orders.services import order_service
 from app.services.email_service import EmailService
 from middleware.vendor_context import require_vendor_context
-from models.database.customer import Customer
 from models.database.vendor import Vendor
 from models.schema.order import OrderCreate, OrderResponse
 
@@ -46,7 +46,7 @@ logger = logging.getLogger(__name__)
 def place_order(
     request: Request,
     order_data: OrderCreate,
-    customer: Customer = Depends(get_current_customer_api),
+    customer: CustomerContext = Depends(get_current_customer_api),
     db: Session = Depends(get_db),
 ):
     """