codemod at least has a typo, and maybe other problems

### What is the problem?

when i run `npx @blitzjs/codemod upgrade-legacy` as instructed in https://blitzjs.com/docs/upgrading-from-framework, I see an error:
`App directory doesn't exit`

On inspection, this is a typo which should read
`App directory doesn't exist`

A deeper issue, though, is that I don't expect the app dir to pre-exist. I'm expecting the code mod to create it, because I am expecting this upgrade to move from pages dir to app dir along with the rest of the upgrade.

### Paste all your error logs here:

```
PASTE_HERE (leave the ``` marks)
```

### Paste all relevant code snippets here:

```
PASTE_HERE (leave the ``` marks)
```

### What are detailed steps to reproduce this?

1.

### Run `blitz -v` and paste the output here:

```
PASTE_HERE (leave the ``` marks)
```

### Please include below any other applicable logs and screenshots that show your problem:

_No response_