chore: add Nix flake

flake.nix

@@ -0,0 +1,90 @@
+{
+  description = "Lightning Decoder";
+
+  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
+    {
+      packages = forAllSystems (system:
+        let
+          pkgs = import nixpkgs { inherit system; };
+          packageJson = builtins.fromJSON (builtins.readFile ./package.json);
+          app = pkgs.buildNpmPackage {
+            pname = packageJson.name;
+            inherit (packageJson) version;
+
+            src = ./.;
+            npmDepsHash = "sha256-TU8anhVBVJUVK9snysRmtmFDs4lzwfjF6v7zdie7QRg=";
+            makeCacheWritable = true;
+            npmFlags = [ "--legacy-peer-deps" ];
+
+            nodejs = pkgs.nodejs_22;
+            nativeBuildInputs = [
+              pkgs.pkg-config
+              pkgs.python3
+            ];
+
+            npm_config_build_from_source = "true";
+
+            installPhase = ''
+              runHook preInstall
+
+              mkdir -p $out/share/${packageJson.name}
+              cp -r build/* $out/share/${packageJson.name}/
+
+              runHook postInstall
+            '';
+          };
+          serve = pkgs.writeShellApplication {
+            name = packageJson.name;
+            runtimeInputs = [ pkgs.python3 ];
+            text = ''
+              host="''${HOST:-127.0.0.1}"
+              port="''${PORT:-5173}"
+
+              cd "${app}/share/${packageJson.name}"
+              echo "Serving ${packageJson.name} at http://$host:$port/"
+              exec python -m http.server "$port" --bind "$host"
+            '';
+          };
+        in
+        {
+          default = app;
+          inherit app serve;
+        });
+
+      apps = forAllSystems (system: {
+        default = {
+          type = "app";
+          program = "${self.packages.${system}.serve}/bin/lightning-decoder";
+        };
+      });
+
+      devShells = forAllSystems (system:
+        let
+          pkgs = import nixpkgs { inherit system; };
+        in
+        {
+          default = pkgs.mkShell {
+            packages = [
+              pkgs.git
+              pkgs.gnumake
+              pkgs.nodejs_22
+              pkgs.pkg-config
+              pkgs.python3
+            ];
+          };
+        });
+    };
+}