fix: expose nixos skill directory to Codex

modules/capabilities/ai.nix

@@ -133,6 +133,6 @@ in
         Every action must justify its context. Minimize tools and skills; prefer targeted queries and bounded output. Ask for readily available large output instead of retrieving it.
       '';
 
-      home.file.".codex/skills/nixos-maintainer/SKILL.md".source = ./skills/nixos-maintainer/SKILL.md;
+      home.file.".codex/skills/nixos-maintainer".source = ./skills/nixos-maintainer;
     };
 }