Move mintlify to devDependencies

[CarlOlson]

As a security tool I don't think there should be any unnecessary dependencies. mintlify seems to have almost no users and being an AI focused tool I'm concerned it could be vibecoded (a security issue for me). It appears to be a dev tool, so it should be moved to devDependencies.

But great project, I was about to make something similar, but you saved me a lot of effort 😅

[lukehinds]

We use mintlify to generate the docs, but there is a case of its perhaps not needed in this repo and is covered

[LotharSee]

👋 I'm using nono-ts in an application I provide to my users. This dependency on mintlify brings in all its sub-dependencies, significantly increasing my application size they have to download. I did a hack to vendor an empty mintlify. It works but it is not great.

Since mintlify is not used at all in nono-ts runtime, it is correct to move it to devDependencies. I opened a PR for it #58 🙇 The diff of package-lock.json nicely shows the amount of files which were installed but not necessary.