flake: move 'devShells' to 'flake/'

.envrc

@@ -5,5 +5,6 @@ fi
 use flake
 
 watch_file ./flake/checks.nix
+watch_file ./flake/dev-shells.nix
 
 eval "$shellHooks"

flake.nix

@@ -122,18 +122,7 @@
 
         checks = import ./flake/checks.nix inputs system;
 
-        devShells = {
+        devShells = import ./flake/dev-shells.nix inputs system;
-          default = pkgs.mkShell {
-            name = "NixOS-config";
-
-            nativeBuildInputs = with pkgs; [
-              gitAndTools.pre-commit
-              nixpkgs-fmt
-            ];
-
-            inherit (self.checks.${system}.pre-commit) shellHook;
-          };
-        };
 
         packages =
           let

flake/dev-shells.nix

@@ -0,0 +1,17 @@
+{ self, nixpkgs, ... }:
+system:
+let
+  pkgs = nixpkgs.legacyPackages.${system};
+in
+{
+  default = pkgs.mkShell {
+    name = "NixOS-config";
+
+    nativeBuildInputs = with pkgs; [
+      gitAndTools.pre-commit
+      nixpkgs-fmt
+    ];
+
+    inherit (self.checks.${system}.pre-commit) shellHook;
+  };
+}