Follows the owner's other projects (sift, tether): nixpkgs pinned to
nixos-26.05, x86_64-linux, the version from the commit. `packages.default`
builds all six binaries with rustPlatform (tests stay in `make gate`),
`packages.tools-image` is deploy/tools-image.nix, and `devShells.default`
has Rust 1.95.0, clippy, rustfmt, cargo-deny and make. No NixOS module
yet: that is M8 (P22).
Checked on straylight: `nix flake check` passes; `nix build` gives
brokerd, bxctl, gatewayd, inferproxy, loopd and toolkit, each printing
its usage; `nix build .#tools-image` and `nix develop` work.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
