Graft: replace dependencies CLI

(claude was used… extensively) Graft replaces dependencies at the store layer, bypassing the normal Nix eval. Inspired by Guix graft. While we do have replaceDependency and system.replaceDependencies I thought it would be nice to have a Guix-style CLI to run grafts more manually and without having to re-evaluate Nix expressions that you may/may-not still have around. Eg: $ nix run nixpkgs/nixos-25.11#curl -- --version curl 8.20.0 (x86_64-pc-linux-gnu) libcurl/8.20.0 OpenSSL/3.6.2 ... $ expor...