pack: add missing type

docs/.vitepress/config.mts

@@ -2,7 +2,7 @@
 import { generateSidebar } from 'vitepress-sidebar'
 import { name, description, repository } from '../../package.json'
 
-const capitalizeFirst = (str) => str.charAt(0).toUpperCase() + str.slice(1)
+const capitalizeFirst = (str: string): string => str.charAt(0).toUpperCase() + str.slice(1)
 
 export default {
   title: capitalizeFirst(name),