migrate dev shell to nix flake

.envrc

@@ -1 +1 @@
-use nix
+use flake

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1746904237,
+        "narHash": "sha256-3e+AVBczosP5dCLQmMoMEogM57gmZ2qrVSrmq9aResQ=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "d89fc19e405cb2d55ce7cc114356846a0ee5e956",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,24 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+  };
+
+  outputs =
+    { nixpkgs, ... }:
+    {
+      devShells =
+        let
+          system = "x86_64-linux";
+          pkgs = import nixpkgs { inherit system; };
+        in
+        {
+          ${system}.default = pkgs.mkShellNoCC {
+            packages = with pkgs; [
+              deno
+              pkgs.nil # Nix language server
+              pkgs.nixfmt-rfc-style
+            ];
+          };
+        };
+    };
+}

shell.nix

@@ -1,7 +0,0 @@
-{
-  pkgs ? import <nixpkgs> { },
-}:
-
-pkgs.mkShell {
-  packages = with pkgs; [ deno ];
-}