refactor(arch): eliminate all cross-module model imports in service layer

Enforce MOD-025/MOD-026 rules: zero top-level cross-module model imports
remain in any service file. All 66 files migrated using deferred import
patterns (method-body, _get_model() helpers, instance-cached self._Model)
and new cross-module service methods in tenancy. Documentation updated
with Pattern 6 (deferred imports), migration plan marked complete, and
violations status reflects 84→0 service-layer violations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/cart/services/cart_service.py

@@ -23,7 +23,6 @@ from app.modules.cart.exceptions import (
 )
 from app.modules.cart.models.cart import CartItem
 from app.modules.catalog.exceptions import ProductNotFoundException
-from app.modules.catalog.models import Product
 from app.utils.money import cents_to_euros
 
 logger = logging.getLogger(__name__)
@@ -146,19 +145,18 @@ class CartService:
         )
 
         # Verify product exists and belongs to store
-        product = (
-            db.query(Product)
-            .filter(
-                and_(
-                    Product.id == product_id,
-                    Product.store_id == store_id,
-                    Product.is_active == True,
-                )
-            )
-            .first()
-        )
+        from app.modules.catalog.services.product_service import product_service
 
-        if not product:
+        try:
+            product = product_service.get_product(db, store_id, product_id)
+        except ProductNotFoundException:
+            logger.error(
+                "[CART_SERVICE] Product not found",
+                extra={"product_id": product_id, "store_id": store_id},
+            )
+            raise ProductNotFoundException(product_id=product_id, store_id=store_id)
+
+        if not product.is_active:
             logger.error(
                 "[CART_SERVICE] Product not found",
                 extra={"product_id": product_id, "store_id": store_id},
@@ -323,19 +321,14 @@ class CartService:
             )
 
         # Verify product still exists and is active
-        product = (
-            db.query(Product)
-            .filter(
-                and_(
-                    Product.id == product_id,
-                    Product.store_id == store_id,
-                    Product.is_active == True,
-                )
-            )
-            .first()
-        )
+        from app.modules.catalog.services.product_service import product_service
 
-        if not product:
+        try:
+            product = product_service.get_product(db, store_id, product_id)
+        except ProductNotFoundException:
+            raise ProductNotFoundException(str(product_id))
+
+        if not product.is_active:
             raise ProductNotFoundException(str(product_id))
 
         # Check inventory