* Add data classes to hold food label information
- Created `GetFoodLabelResponse` data class to represent food label details
- Updated `GetFoodResponse` to include `label` property of type `GetFoodLabelResponse`
* Add backend to sort items in shopping lists by label
* Add UI code to sort items in shopping lists by label
* Use label from ShoppingListItem instead of Food
* Use list for ShoppingListItems and labels storage
* Fix incorrect routing code
* Only add DefaultLabel if there are items with a label
* Small improvements to comments and formatting
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