feat: add nix flake (#593)

Co-authored-by: Samuel Gunter <29130894+Samathingamajig@users.noreply.github.com>

flake.nix

@@ -0,0 +1,32 @@
+{
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs =
+    inputs:
+    inputs.flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = (import (inputs.nixpkgs) { inherit system; });
+      in
+      {
+        formatter = pkgs.nixfmt-rfc-style;
+
+        devShell = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            nodejs_20 # v20.19.0
+            pnpm_10 # v10.8.1
+            just
+          ];
+
+          shellHook = ''
+            echo "UTRP Nix Flake Environment Loaded"
+            echo "Node: $(node --version)"
+            echo "pnpm: $(pnpm --version)"
+          '';
+        };
+      }
+    );
+}