feat: setup nix dev shell

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -14,3 +14,8 @@
 compile_commands.json
 .clangd/
 .cache/
+
+# nix
+result
+result-*
+.direnv/

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1777268161,
+        "narHash": "sha256-bxrdOn8SCOv8tN4JbTF/TXq7kjo9ag4M+C8yzzIRYbE=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "1c3fe55ad329cbcb28471bb30f05c9827f724c76",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,40 @@
+{
+  description = "QMK dev shell";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+      forAllSystems = nixpkgs.lib.genAttrs systems;
+    in
+    {
+      devShells = forAllSystems (
+        system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+        in
+        {
+          default = pkgs.mkShell {
+            packages = with pkgs; [
+              just
+              pre-commit
+              gnumake
+              gcc-arm-embedded
+              qmk
+              dfu-util
+              clang-tools
+            ];
+          };
+        }
+      );
+
+      formatter = forAllSystems (system: nixpkgs.legacyPackages.${system}.nixfmt);
+    };
+}