Use the upstream Moonshine NixOS module when #544393 lands

[repparw]

Blocker

Nixpkgs PR #544393 adds the Moonshine NixOS module.

Cleanup

In modules/aspects/streaming/default.nix:

• remove the external module import
• remove the external Moonshine input if no longer needed
• adapt openFirewall to firewallInterfaces
• remove the local uid option
• validate the existing applications and Steam wrapper

The Moonshine package migration is already handled separately; this issue tracks only the module migration.