Restore support for package managers other than `npm`

In https://github.com/arethetypeswrong/arethetypeswrong.github.io/pull/180, support for `pnpm`/`yarn` was removed, for reasons that aren't super clear (I guess there was a bug with the support? https://github.com/arethetypeswrong/arethetypeswrong.github.io/issues/179).

I'd propose support for packing with `pnpm`/`yarn` be restored. If not via automatic detection, at least to the point of being able to specify a way to use `attw` in CI neatly. For example, while `attw $(npm pack)` is documented, and works fine, `attw $(pnpm pack)` fails, with:

```plaintext
error while checking file:
ENOENT: no such file or directory, open '📦'
```

首先重现文档中记录的 `attw $(npm pack)` 流程以及失败的 `attw $(pnpm pack)` 命令，然后检查 `attw` CLI 入口点及其对 package 文件参数的处理方式。完成的标准是支持使用 pnpm 和 yarn 进行打包，或者提供明确的 CI 调用方式，同时不将 pnpm 的 `📦` 输出当作文件名。

由索引模型根据 Issue 内容生成。