flake: add nix package output

flake.nix

@@ -0,0 +1,32 @@
+{
+  description = "tracker: single-binary project tracker (hackerman edition)";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";
+
+  outputs = { self, nixpkgs }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forAllSystems = nixpkgs.lib.genAttrs systems;
+    in
+    {
+      packages = forAllSystems (system:
+        let pkgs = nixpkgs.legacyPackages.${system}; in
+        rec {
+          tracker = pkgs.buildGoModule {
+            pname = "tracker";
+            version = "0.1.0";
+            src = self;
+            env.CGO_ENABLED = "0";
+            vendorHash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
+          };
+          default = tracker;
+        });
+
+      apps = forAllSystems (system: {
+        default = {
+          type = "app";
+          program = "${self.packages.${system}.default}/bin/tracker";
+        };
+      });
+    };
+}