refactor: restructure item interfaces and update related components

- Renamed LineItem interface to Item and adjusted properties accordingly.
- Updated CreateItemData and UpdateItemData interfaces to reflect new structure.
- Modified components to use the new Item interface, removing nested lines.
- Adjusted data binding in item configuration, main data, and other related components.
- Simplified item creation and editing logic by removing unnecessary nesting.
- Ensured all references to line items are updated to reflect the new structure.

backend/api/v1/modules/a76/items/__init__.py

@@ -4,16 +4,14 @@ Items module - Annex 76 Compliance
 
 # Import models in correct order to avoid circular dependencies
 # LineItem must be imported before models that reference it
-from .line_items.models import LineItem
 from .line_financials.models import LineFinancial
 from .line_quantities.models import LineQuantity
 from .line_customs.models import LineCustom
 from .line_descriptions.models import LineDescription
 from .line_references.models import LineReference
-from .models import Item, CTMReceipt, SubassemblyEntry
+from .models import LineItem, CTMReceipt, SubassemblyEntry
 
 __all__ = [
-    "Item",
     "LineItem",
     "LineFinancial",
     "LineQuantity",