让 Rollup 查找到外部模块

npm i -D @rollup/plugin-node-resolve

// rollup.config.mjs
import resolve from '@rollup/plugin-node-resolve'

export default {
	input: 'src/main.js',
	output: {
		file: './dist/bundle.js',
		format: 'cjs'
	},
	plugins: [resolve()]
}