fix: flake.nix typo, generate.sh word-splitting, README accuracy

- flake.nix: fix gettex → gettext typo, restore codex package
- generate.sh: replace ls-based loop with direct glob (word-splitting safe)
- README.md: fix AGENTS.md source column (rules/*.md only, not CLAUDE.md)

flake.nix

@@ -7,7 +7,11 @@
     in {
       devShells = forAllSystems (pkgs: {
         default = pkgs.mkShell {
-          packages = [ pkgs.yq-go pkgs.gettext pkgs.codex ];
+          packages = with pkgs; [
+            yq-go
+            gettext
+            codex
+          ];
         };
       });
     };