docs(nix): require natu checks

AGENTS.md

@@ -43,8 +43,6 @@
 - Stage new files that Nix discovers through flake evaluation before testing.
   Flake evaluation ignores untracked files, so auto-loaded modules must be tracked before
   `nixos-rebuild --flake` can see them.
-- After modifying Nix files, run `bazel run //src/natu:natu -- <paths>`.
-  Pass every modified Nix path as an argument.
 
 ## General guidelines
 

src/skills/style/nix/SKILL.md

@@ -12,7 +12,10 @@ After editing Nix files, run:
 
 ```bash
 nix run .#fix
+bazel run //src/natu:natu -- <modified-nix-paths>
 ```
 
-Finish when `nix run .#fix` succeeds and the Nix change follows the loaded rules.
-If the command fails, report the failure.
+Pass every modified Nix path to Natu.
+
+Finish when both commands succeed and the Nix change follows the loaded rules.
+If a command fails, report the failure.