feat: add brands and variant categories management

- Implemented CRUD operations for brands and variant categories in the API.
- Created UI components for managing brands and variant categories, including listing, creating, editing, and deleting.
- Enhanced the sidebar navigation to include links for brands and variant categories.
- Updated the categories API to support pagination and filtering.
- Added validation for brand and variant category names.
- Integrated toast notifications for user feedback on actions.

Frontend/erp-system/lib/validations/master-data.ts

@@ -50,3 +50,25 @@ export function validateCategoryName(name: string): Record<string, string> {
   if (!name.trim()) errors.name = "Category name is required"
   return errors
 }
+
+export function validateBrandName(name: string): Record<string, string> {
+  const errors: Record<string, string> = {}
+  if (!name.trim()) errors.name = "Brand name is required"
+  return errors
+}
+
+export function validateVariantCategoryName(name: string): Record<string, string> {
+  const errors: Record<string, string> = {}
+  if (!name.trim()) errors.name = "Category name is required"
+  return errors
+}
+
+export function validateVariantItemForm(input: {
+  categoryId: number | null
+  hasVariants: boolean
+}): Record<string, string> {
+  const errors: Record<string, string> = {}
+  if (!input.categoryId) errors.categoryId = "Select a category"
+  if (!input.hasVariants) errors.variants = "Check at least one variant category and add its values"
+  return errors
+}