fix(ai-cli): install current upstream Codex and Claude releases

- Pin official Codex 0.161.0 and Claude Code 2.1.292 binaries
- Preserve Codex helpers and Claude's NixOS compatibility wrapper
- Add an updater for stable upstream versions and checksums
- Document CLI updates independently of stable NixOS inputs

flake.nix

@@ -19,6 +19,14 @@
       ...
     }:
     {
+      # Build the CLI packages separately before switching a host.
+      packages.x86_64-linux = import ./packages/ai-cli.nix {
+        pkgs = import nixpkgs {
+          system = "x86_64-linux";
+          config.allowUnfree = true;
+        };
+      };
+
       nixosConfigurations = {
         t450s = nixpkgs.lib.nixosSystem {
           specialArgs.unstable = import nixpkgs-unstable {