feat: flake interface definition

hosts/default.nix

@@ -0,0 +1,9 @@
+inputs @ {nixpkgs, ...}:
+let
+  inherit (nixpkgs) lib;
+  isDir = _name: type: type == "directory";
+  directoriesAsModules = dir: (builtins.mapAttrs
+    (name: _value: dir + "/${name}")
+    (lib.filterAttrs isDir (builtins.readDir dir))
+  );
+in directoriesAsModules ./.

hosts/git.example.tld/default.nix

@@ -0,0 +1,8 @@
+inputs @ {config, ...}:
+let
+  allusers = (import ../../users) inputs;
+{
+  users.users = {
+    inherit (allUsers) alice bob;
+  }
+}

hosts/web.example.org/default.nix

@@ -0,0 +1,8 @@
+inputs @ {config, ...}:
+let
+  allusers = (import ../../users) inputs;
+{
+  users.users = {
+    inherit (allUsers) alice bob mallory root;
+  }
+}