Add flake.nix wrapping shell.nix

Lets `nix develop` users enter the same dev environment as `nix-shell`.
The flake's devShell imports ./shell.nix, so both entry points stay in
sync with a single dependency list.

No flake.lock is committed: inputs float on nixos-unstable, matching the
existing shell.nix behaviour (which already tracks <nixpkgs>).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 2 people

.gitignore

@@ -8,3 +8,4 @@ gcode2ps
 test-out/
 compile_commands.json
 .cache
+flake.lock

flake.nix

@@ -0,0 +1,14 @@
+{
+  description = "BeagleG dev shell";
+
+  # nixos-unstable @ 2026-06-26
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/e73de5be04e0eff4190a1432b946d469c794e7b4";
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let pkgs = import nixpkgs { inherit system; };
+      in {
+        devShells.default = import ./shell.nix { inherit pkgs; };
+      });
+}