nix: flatten homeModule implementation

nix/homeModules/common/direnv.nix

@@ -0,0 +1,13 @@
+{ config, ... }:
+
+{
+  programs.direnv = {
+    nix-direnv.enable = true;
+    config = builtins.fromTOML ''
+      [whitelist]
+      prefix = [ "${config.home.homeDirectory}/.dotfiles" ]
+      [global]
+      strict_env = true
+    '';
+  };
+}