Add direnv and Nix flake files.

.envrc

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+use flake

flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1678901627,
+        "narHash": "sha256-U02riOqrKKzwjsxc/400XnElV+UtPUQWpANPlyazjH0=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "93a2b84fc4b70d9e089d029deacc3583435c2ed6",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1679410443,
+        "narHash": "sha256-xDHO/jixWD+y5pmW5+2q4Z4O/I/nA4MAa30svnZKK+M=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c9ece0059f42e0ab53ac870104ca4049df41b133",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        devShells.default = import ./shell.nix { inherit pkgs; };
+      }
+    );
+}

shell.nix

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+{ pkgs ? import <nixpkgs> { } }:
+
+with pkgs;
+
+mkShell rec {
+  packages = [ nodejs nodePackages.pnpm ];
+}