Layer the remaining flake outputs onto the build: a default app pointing at
the compiled binary, a dev shell exposing the pinned Bun, biome, and bun2nix,
a `use flake` .envrc for direnv, and a checks set aggregating the Bun test
tiers, a build-seam smoke check against the Nix-built binary, and biome lint
through the treefmt-nix flake-parts module.
The dev shell and the build share the one pinned nixpkgs-bun input so Bun
cannot drift between them. treefmt's biome reuses the repo's biome.json with
VCS disabled for the sandbox, and packages/core/src/index_test.ts is
reformatted by biome so the new lint gate is green.
Add a flake-parts flake whose default package Bun-compiles the kitchen
CLI into a self-contained native binary, built in the sandbox with
dependencies vendored by bun2nix.
Bun is pinned via a dedicated nixpkgs-bun input (Bun 1.3.13) that
bun2nix follows, so nixpkgs can track unstable without moving the
compile toolchain onto a release that emits empty binaries.
bun2nix is both a flake input and an npm devDependency, and a
postinstall hook keeps the checked-in bun.nix in sync with the lockfile.
