refactor: move transaction management from services to API endpoints

- Services now use db.flush() instead of db.commit() for database operations
- API endpoints handle transaction commit after service calls
- Remove db.rollback() from services (let exception handlers manage this)
- Ensures consistent transaction boundaries at API layer

This pattern gives API endpoints full control over when to commit,
allowing for better error handling and potential multi-operation transactions.

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

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

app/services/inventory_service.py

@@ -62,7 +62,7 @@ class InventoryService:
                 old_qty = existing.quantity
                 existing.quantity = inventory_data.quantity
                 existing.updated_at = datetime.now(UTC)
-                db.commit()
+                db.flush()
                 db.refresh(existing)
 
                 logger.info(
@@ -79,7 +79,7 @@ class InventoryService:
                 gtin=product.marketplace_product.gtin,  # Optional reference
             )
             db.add(new_inventory)
-            db.commit()
+            db.flush()
             db.refresh(new_inventory)
 
             logger.info(
@@ -143,7 +143,7 @@ class InventoryService:
                     gtin=product.marketplace_product.gtin,
                 )
                 db.add(new_inventory)
-                db.commit()
+                db.flush()
                 db.refresh(new_inventory)
 
                 logger.info(
@@ -165,7 +165,7 @@ class InventoryService:
 
             existing.quantity = new_qty
             existing.updated_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             db.refresh(existing)
 
             logger.info(
@@ -227,7 +227,7 @@ class InventoryService:
             # Reserve inventory
             inventory.reserved_quantity += reserve_data.quantity
             inventory.updated_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             db.refresh(inventory)
 
             logger.info(
@@ -287,7 +287,7 @@ class InventoryService:
                 inventory.reserved_quantity -= reserve_data.quantity
 
             inventory.updated_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             db.refresh(inventory)
 
             logger.info(
@@ -353,7 +353,7 @@ class InventoryService:
                 0, inventory.reserved_quantity - reserve_data.quantity
             )
             inventory.updated_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             db.refresh(inventory)
 
             logger.info(
@@ -507,7 +507,7 @@ class InventoryService:
                 inventory.location = self._validate_location(inventory_update.location)
 
             inventory.updated_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             db.refresh(inventory)
 
             logger.info(f"Updated inventory {inventory_id}")
@@ -535,7 +535,7 @@ class InventoryService:
                 raise InventoryNotFoundException(f"Inventory {inventory_id} not found")
 
             db.delete(inventory)
-            db.commit()
+            db.flush()
 
             logger.info(f"Deleted inventory {inventory_id}")
             return True