Amend @types/node constraint

### Which package(s) are affected?

SSR (@lit-labs/ssr)

### Description

lit-labs/ssr runs fine under node 25 ^ 26, but can't be installed alongside the appropriate `@types/node` package due to the version constraint excluding the package targeting node 25 & 26.

Start in the SSR (@lit-labs/ssr) package metadata and inspect the @types/node version constraint. Adjust the constraint so the package targeting Node 25 and 26 can be installed alongside SSR, then verify the dependency installation for those Node typings versions.

Written by the indexing model from the issue text.