feat(i18n): compute bilingual label on giving/ministry/expense-category lookups

APP/src/app/features/giving/models/giving.model.ts

@@ -18,6 +18,8 @@ export interface GivingCategoryDto {
   description_zh: string | null;
   isActive: boolean;
   sortOrder: number;
+  /** Display-only bilingual label, computed in the API service. */
+  label?: string;
 }
 export interface CreateGivingCategoryRequest {
   name_en: string;