fix(main-data): implement automatic class description updates based on class_id changes

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

@@ -8,6 +8,7 @@
 	import TariffFractionDialog from './tariff-fraction-dialog.svelte';
 	import ClassDialog from './class-dialog.svelte';
     import type { LineItem, LineQuantities, LineFinancials, LineCustoms } from '$lib/api/dashboard/a76/items';
+	import { companyStore } from '$lib/stores/company.svelte';
 
     let {
         lineItem = $bindable(),
@@ -26,6 +27,9 @@
 	let showCountryDialog = $state(false);
 	let showFractionDialog = $state(false);
 
+	// Track previous class_id to detect changes
+	let previousClassId = $state<number | undefined>(undefined);
+
 	// Initialize from existing data
 	$effect(() => {
 		if (lineItem.class_code) {
@@ -33,12 +37,66 @@
 		}
 	});
 
+	// Watch for class_id changes and update descriptions automatically
+	$effect(() => {
+		const currentClassId = lineItem.class_id;
+		const activeCompanyId = companyStore?.activeCompany?.id;
+		
+		// Only fetch if class_id changed, is valid, and we have a company
+		if (currentClassId && currentClassId !== previousClassId && activeCompanyId) {
+			previousClassId = currentClassId;
+			
+			// Fetch all classes and find the one with matching ID
+			fetch(`/api-sveltekit/classes?company_id=${activeCompanyId}&limit=100`)
+				.then(response => {
+					if (response.ok) {
+						return response.json();
+					}
+					throw new Error('Failed to fetch classes');
+				})
+				.then(data => {
+					const classes = data.items || [];
+					const classItem = classes.find((c: any) => c.id === currentClassId);
+					
+					if (classItem) {
+						// Store the code and description in the lineItem for display
+						(lineItem as any).class_code = classItem.class_code;
+						(lineItem as any).class_unit_of_measure = classItem.unit_of_measure;
+						(lineItem as any).class_description = classItem.description_es || classItem.description_en;
+						
+						// Update description fields if description object exists
+						if ((lineItem as any).description) {
+							if (classItem.description_es) {
+								(lineItem as any).description.description_spanish = classItem.description_es;
+							}
+							if (classItem.description_en) {
+								(lineItem as any).description.description_english = classItem.description_en;
+							}
+						}
+					}
+				})
+				.catch(error => {
+					console.error('Error fetching class data:', error);
+				});
+		}
+	});
+
 	function handleClassSelect(classItem: any) {
 		lineItem.class_id = classItem.id;
 		// Store the unit of measure and description for display
 		(lineItem as any).class_unit_of_measure = classItem.unit_of_measure;
 		(lineItem as any).class_code = classItem.class_code;
 		(lineItem as any).class_description = classItem.description_es || classItem.description_en;
+		
+		// Update description fields if description object exists
+		if ((lineItem as any).description) {
+			if (classItem.description_es) {
+				(lineItem as any).description.description_spanish = classItem.description_es;
+			}
+			if (classItem.description_en) {
+				(lineItem as any).description.description_english = classItem.description_en;
+			}
+		}
 	}
 
 	function handleUnitSelect(unit: any) {