feat(nix): add initial Nix flake configuration and lock file for package management

default.nix

@@ -0,0 +1,4 @@
+let
+  flake = builtins.getFlake "git+file://${builtins.toString ./.}";
+in
+flake.packages.${builtins.currentSystem}.default

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1768302833,
+        "narHash": "sha256-h5bRFy9bco+8QcK7rGoOiqMxMbmn21moTACofNLRMP4=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "61db79b0c6b838d9894923920b612048e1201926",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,36 @@
+{
+  description = "Global packages for dotfiles";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      systems = [
+        "x86_64-darwin"
+        "aarch64-darwin"
+        "x86_64-linux"
+        "aarch64-linux"
+      ];
+      forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f system);
+    in
+    {
+      packages = forAllSystems (
+        system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+        in
+        {
+          default = pkgs.buildEnv {
+            name = "dotfiles-packages";
+            paths = [
+              pkgs.nil
+              pkgs.nixfmt
+            ];
+          };
+        }
+      );
+    };
+}