feat(users, contents): extend admin update functionality and role management

- Added `moderator` role to `User` type for improved role assignment flexibility.
- Introduced `updateAdmin` method in user and content services to handle partial admin-specific updates.
- Enhanced `Content` type with `categoryId` and `iconUrl` to support richer categorization.

frontend/src/services/content.service.ts

@@ -65,4 +65,9 @@ export const ContentService = {
 	async removeAdmin(id: string): Promise<void> {
 		await api.delete(`/contents/${id}/admin`);
 	},
+
+	async updateAdmin(id: string, update: Partial<Content>): Promise<Content> {
+		const { data } = await api.patch<Content>(`/contents/${id}/admin`, update);
+		return data;
+	},
 };