fix: handle `output: export` with `use client` (#47635)
This PR removes usage of `appPaths` in favor of `hasAppDir` to avoid the
issue where export does not read app manifest.
Fixes the error:
```
TypeError: Cannot read properties of undefined (reading 'cssModules')
```
fix NEXT-885 ([link](https://linear.app/vercel/issue/NEXT-885))
