fix: autoDir for packages and flat directories

lib/autoDir.nix

@@ -1,10 +1,21 @@
 lib:
 
-# import package.nix from each subdirectory in dir as attribute set
+# auto-discover nix modules from a directory
+# - flat .nix files (excluding default.nix) are imported directly
+# - subdirectories containing package.nix are imported via package.nix
 dir:
 let
   readDir = builtins.readDir dir;
-  dirs = lib.attrNames (lib.filterAttrs (_: type: type == "directory") readDir);
-  packages = lib.filter (name: builtins.pathExists (dir + "/${name}/package.nix")) dirs;
+
+  files = lib.filterAttrs (
+    name: type: type == "regular" && lib.hasSuffix ".nix" name && name != "default.nix"
+  ) readDir;
+
+  dirs = lib.filterAttrs (
+    name: type: type == "directory" && builtins.pathExists (dir + "/${name}/package.nix")
+  ) readDir;
 in
-lib.genAttrs packages (name: import (dir + "/${name}/package.nix"))
+lib.mapAttrs' (
+  name: _: lib.nameValuePair (lib.removeSuffix ".nix" name) (import (dir + "/${name}"))
+) files
+// lib.mapAttrs (name: _: import (dir + "/${name}/package.nix")) dirs