feat: add automatic stock synchronization for orders

Implements order-inventory integration that automatically manages stock
when order status changes:
- processing: reserves inventory for order items
- shipped: fulfills (deducts) from stock
- cancelled: releases reserved inventory

Creates OrderInventoryService to orchestrate operations between
OrderService and InventoryService. Placeholder products (unmatched
Letzshop items) are skipped. Inventory errors are logged but don't
block order status updates.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/services/order_service.py

@@ -31,6 +31,7 @@ from app.exceptions import (
     ValidationException,
 )
 from app.services.order_item_exception_service import order_item_exception_service
+from app.services.order_inventory_service import order_inventory_service
 from app.services.subscription_service import (
     subscription_service,
     TierLimitExceededException,
@@ -963,6 +964,11 @@ class OrderService:
         """
         Update order status and tracking information.
 
+        This method now includes automatic inventory management:
+        - processing: Reserves inventory for order items
+        - shipped: Fulfills (deducts) inventory
+        - cancelled: Releases reserved inventory
+
         Args:
             db: Database session
             vendor_id: Vendor ID
@@ -975,9 +981,9 @@ class OrderService:
         order = self.get_order(db, vendor_id, order_id)
 
         now = datetime.now(UTC)
+        old_status = order.status
 
         if order_update.status:
-            old_status = order.status
             order.status = order_update.status
 
             # Update timestamps based on status
@@ -990,6 +996,29 @@ class OrderService:
             elif order_update.status == "cancelled" and not order.cancelled_at:
                 order.cancelled_at = now
 
+            # Handle inventory operations based on status change
+            try:
+                inventory_result = order_inventory_service.handle_status_change(
+                    db=db,
+                    vendor_id=vendor_id,
+                    order_id=order_id,
+                    old_status=old_status,
+                    new_status=order_update.status,
+                )
+                if inventory_result:
+                    logger.info(
+                        f"Order {order.order_number} inventory update: "
+                        f"{inventory_result.get('reserved_count', 0)} reserved, "
+                        f"{inventory_result.get('fulfilled_count', 0)} fulfilled, "
+                        f"{inventory_result.get('released_count', 0)} released"
+                    )
+            except Exception as e:
+                # Log inventory errors but don't fail the status update
+                # Inventory can be adjusted manually if needed
+                logger.warning(
+                    f"Order {order.order_number} inventory operation failed: {e}"
+                )
+
         if order_update.tracking_number:
             order.tracking_number = order_update.tracking_number