feat: update item response schema and refactor item creation logic for improved payload structure

frontend/src/lib/components/dashboard/invoices/edit/items/fa/main-data.svelte

@@ -9,7 +9,7 @@
 	import ClassDialog from './class-dialog.svelte';
 	import type { Item, LineQuantities, LineFinancials, LineCustoms } from '$lib/api/dashboard/a76/items';
 	import type { Invoice } from '$lib/api/dashboard/a76/invoices';
-	import { companyStore } from '$lib/stores/company.svelte';
+	import { companyStore } from '$lib/stores/company.svelte';	
 
     let {
         lineItem = $bindable(),
@@ -110,10 +110,10 @@
 				(lineItem as any).description.description_english = classItem.description_en;
 			}
 		}
-	}
+	};
 
 	function handleUnitSelect(unit: any) {
-		lineItem.unit_of_measure = unit.id;
+		lineItem.unit_of_measure = unit.id;				
 		// Store unit code for display
 		(lineItem as any).unit_code = unit.code;
 		(lineItem as any).unit_description = unit.description || unit.description_en;

frontend/src/lib/components/dashboard/invoices/edit/items/items-tab-form.svelte

@@ -501,19 +501,26 @@
 
 		isSavingPreset = true;
 		try {
-			// Each item in builderItems is already a LineItem (no nested lines)
-			const cleanedItems = builderItems.map((item: Item, idx: number) => {
+			// We group everything as items for the template
+			const lines = builderItems.map((item: Item, idx: number) => {
 				return {
 					...cleanLineData(item),
-					line_number: item.line_number || idx + 1,
+					line_number: item.line_number || idx + 1, // Ensure line_number is present
 					id: undefined // Ensure no IDs are saved in the preset
 				};
 			});
 
+			const payloadItems = [
+				{
+					reference_number: builderItems[0]?.reference_number || undefined,
+					lines: lines
+				}
+			] as any;
+
 			await itemPresetsApi.create(activeCompanyId, {
 				name: createPresetName.trim(),
 				description: createPresetDescription.trim() || undefined,
-				items: cleanedItems
+				items: payloadItems
 			});
 
 			createPresetName = '';