move atuin from nixpkgs to its flake

flake.nix

@@ -9,6 +9,7 @@
           url = "github:nix-community/home-manager/release-25.11";
           inputs.nixpkgs.follows = "nixpkgs";
         };
+        atuin.url = "github:atuinsh/atuin/v18.13.3";
     };
 
     outputs = { self, nixpkgs,  nix-flatpak, systems, home-manager, ... } @ inputs: let
@@ -21,6 +22,9 @@
             import nixpkgs {
               inherit system;
               config.allowUnfree = true;
+              overlays = [
+                inputs.atuin.overlays.default
+              ];
             }
         );
 
@@ -34,6 +38,9 @@
             modules = [
               nix-flatpak.nixosModules.nix-flatpak
               ./hosts/limgrave/nixos
+              ({ ... }: {
+                nixpkgs.overlays = [ inputs.atuin.overlays.default ];
+              })
             ];
           };
         };
@@ -48,4 +55,4 @@
           };
         };
     };
-}
+}