refactor: complete overhaul

parts/config/devshells.nix

@@ -0,0 +1,22 @@
+{
+  pkgs,
+  config,
+  ...
+}: {
+  devShells = {
+    default = pkgs.mkShell {
+      packages = builtins.attrValues {
+        inherit
+          (pkgs)
+          age
+          alejandra
+          just
+          nil
+          sops
+          ssh-to-age
+          ;
+      };
+      shellHook = "${config.pre-commit.installationScript}";
+    };
+  };
+}