Update $app/stores page.stuff to use App.Stuff

[tmarnet]

Following #3670, page.stuff from $app/stores should use App.Stuff instead of the old Record<string, any>

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[changeset-bot]

🦋 Changeset detected

Latest commit: 27db4b9

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[Rich-Harris]

thank you!