refactor: nix flake (#625)

* chore(nix): update flake

* chore(nix): remove just and update comment

* chore(nix): update node version + volta config

* refactor: nix flake

flake.nix

@@ -1,20 +1,25 @@
 {
   inputs = {
-    flake-utils.url = "github:numtide/flake-utils";
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
   };
 
   outputs =
-    inputs:
-    inputs.flake-utils.lib.eachDefaultSystem (
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
       system:
       let
-        pkgs = (import (inputs.nixpkgs) { inherit system; });
+        pkgs = (import nixpkgs { inherit system; });
       in
       {
         formatter = pkgs.nixfmt-rfc-style;
 
-        devShell = pkgs.mkShell {
+        devShells.default = pkgs.mkShell {
+          name = "utrp-dev";
           buildInputs = with pkgs; [
             nodejs_20 # v20.19.4
             pnpm_10 # v10.14.0