Move librewolf out of the bare package list into its own module declaring
`local.librewolf.package` (default pkgs.librewolf), mirroring texlive. Lets a
consumer swap the wrapped package — extraPolicies/extraPrefs — to share
extensions and an about:config baseline across profiles without editing the
module.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
