tatara-pkgs — nixpkgs, fully expressed in tatara-lisp

Two things live together:

1. PackageSet trait — backend-agnostic view of a package universe. Every backend (nixpkgs bridge, tatara-lisp-authored set, overlay of either) answers get(name) -> Option<Derivation> + names() -> Vec<String>.

2. Synthesizer — a MultiSynthesizer that walks a PackageSet and emits one tatara-lisp .tl file per package. tend drives this: on a nixpkgs commit bump, the generator regenerates the mirror tree; each package becomes a typed (defderivation …) that realizes to the same /nix/store/... path nixpkgs would produce.

nixpkgs ──tend sync──►  PackageSet (NixpkgsBridge)
                             │
                             ▼ MultiSynthesizer::generate_all
                        Vec<Artifact>  (`hello.tl`, `bash.tl`, …)
                             │
                             ▼ disk
                        pleme-io/nixpkgs-tl/
                             │
                             ▼ tatara-eval + tatara-nix::Realizer
                        /nix/store/<hash>-<name>  (same path nixpkgs builds)

The gradient: today a tatara-lisp file is a bridge wrapper; tomorrow the hot-path packages (stdenv, coreutils, bash, kernel) transliterate to pure tatara-lisp and stop bridging. The typed surface doesn't change.