Improve nix setup

flake.nix

@@ -1,41 +1,22 @@
 {
   description = "lwn-sub-snoozer";
   inputs = {
-    flake-utils.url = "github:numtide/flake-utils";
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
   };
 
   outputs = {
     self,
     nixpkgs,
-    flake-utils,
-  }:
-    flake-utils.lib.eachDefaultSystem (system: let
-      pkgs = nixpkgs.legacyPackages.${system};
-    in {
-      packages = {
-        default = self.packages.${system}.myapp;
-      };
-      # $ nix develop
-      devShells.default = pkgs.mkShell {
-        LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [pkgs.openssl];
-        packages = [
-          pkgs.pkg-config
-          pkgs.openssl
-          pkgs.postgresql
-
-          # Nix
-          pkgs.nixpkgs-fmt
-          pkgs.nil
-          pkgs.nixd
-          pkgs.alejandra
-
-          # Rust
-          pkgs.rustfmt
-          pkgs.rustc
-          pkgs.cargo
-          pkgs.rust-analyzer
-        ];
-      };
+  }: let
+    supportedSystems = ["x86_64-linux"];
+    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+    pkgsFor = nixpkgs.legacyPackages;
+  in {
+    packages = forAllSystems (system: {
+      default = pkgsFor.${system}.callPackage ./. {};
     });
+    devShells = forAllSystems (system: {
+      default = pkgsFor.${system}.callPackage ./shell.nix {};
+    });
+  };
 }