chore: upgrade deps and use app.config

[atinux]

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Currently having two issues:

This is related to the renaming on nuxt/framework#6864 and the fact that Nuxt Content still use RC8 for nuxt/kit: https://github.com/nuxt/content/blob/main/package.json#L45

Might be fixed in RC9, this is not a blocker since only a warning.

The other issue is regarding the design tokens @Tahul

Leading to a 500 error:

[atinux]

The app.config.ts needs edge channel @pi0

[Tahul]

@atinux ; fixed design tokens usage & <Markdown> moved to <ContentSlot />.

I wish we could do something about that warning though.