[M7] flake: distribution bundles + non-NixOS wrapper

CHANGELOG.md

@@ -398,3 +398,40 @@ All notable changes to cargoxx will be documented in this file.
 - Fix: `-Wparentheses` warning in `looks_like_missing_attribute`
   (`src/resolver/nixpkgs_probe.cpp:34`) — explicitly parenthesize the
   `&&` clause inside `||`.
+- M7 `cargoxx-bin` wraps the binary with `makeWrapper` to lock its
+  runtime CLI dependencies — `nix`, `cmake`, `ninja`, `curl`, `git`
+  — onto `PATH`. Previously cargoxx silently relied on the user's
+  ambient PATH, so it broke whenever invoked outside a `nix develop`
+  shell. The wrapped binary works under `env -i` with a minimal PATH.
+- M7 the wrapper also `--set-default`s `NIX_CONFIG` to
+  `experimental-features = nix-command flakes` and
+  `build-users-group =`. Without this, the bundled `pkgs.nix`
+  defaults to the multi-user daemon model and fails on non-NixOS
+  hosts (`error: the group 'nixbld' specified in 'build-users-group'
+  does not exist`). `--set-default` lets a user with a properly-
+  configured nix daemon override by exporting `NIX_CONFIG=...`
+  before invoking cargoxx. Verified end-to-end in `archlinux:latest`
+  via `docker run`: install the `.pkg.tar.zst`, `cargoxx new demo &&
+  cargoxx add fmt` runs the resolver chain through verify-link
+  cmake/ninja and writes the dep without error.
+- M7 packaging functions exposed as a stable `to*` library and as
+  ready-to-build flake packages, mirroring the
+  `github:NixOS/bundlers` naming. Available as both
+  `packages.<format>` (for `nix build .#<format>`) and
+  `lib.to<Format>` (for downstream flakes to package their own
+  derivations):
+  - `toAppImage` / `packages.appimage` — Linux AppImage (~207 MB)
+  - `toDockerImage` / `packages.dockerImage` — `docker load`-able
+    tar.gz (~213 MB)
+  - `toDEB` / `packages.deb` — Debian `.deb` (~211 MB)
+  - `toRPM` / `packages.rpm` — Red Hat `.rpm` (~212 MB)
+  - `toArchPkg` / `packages.archpkg` — Arch `.pkg.tar.zst`
+    (~196 MB), implemented locally because no NixOS bundler exists.
+    Builds a closure via `pkgs.closureInfo`, lays it under
+    `/nix/store`, drops a `/usr/bin/<mainProgram>` symlink, writes
+    `.PKGINFO` from `drv.pname`/`drv.version`/`drv.meta`, and packs
+    with `bsdtar --zstd`. Generic — works for any derivation with
+    a `bin/<mainProgram>` and the usual `pname`/`version` attrs.
+  Added `inputs.bundlers.url = "github:NixOS/bundlers"` (with
+  `inputs.nixpkgs.follows = "nixpkgs"`) to keep the closure aligned
+  with the project's pinned nixpkgs.