feat: add category/tag management UI with ColoredItemCombobox

- ColoredItemCombobox component with search, color swatches, inline creation
- Replace text inputs with combobox dropdowns for category and tag selection
- API methods for categories/tags CRUD
- TypeScript types for NewsCategory, NewsTag
- i18n keys for combobox (ru, en)

src/components/admin/index.ts

@@ -1,5 +1,6 @@
 // Components
 export * from './AdminBackButton';
+export * from './ColoredItemCombobox';
 export * from './icons';
 export * from './Toggle';
 export * from './SettingInput';