docs: update links to point to new site

[arichardsmith]

Update (some) of the links pointing to the old preview site as mentioned in #13982.

This updates all the links in documentation/ and packages/svelte/messages, but doesn't touch others present in packages/svelte/ or fix the original link in that issue.

I didn't add a changeset as it was only docs. But, if the error messages have changed, would that need a changeset?

[changeset-bot]

⚠️ No Changeset found

Latest commit: ffdd3e0

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[vercel]

@dummdidumm is attempting to deploy a commit to the Svelte Team on Vercel.

A member of the Team first needs to authorize it.

[pkg-pr-new]

pnpm add https://pkg.pr.new/svelte@13986

commit: ffdd3e0

[dummdidumm]

thank you!