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)

generate.sh

@@ -254,7 +254,7 @@ TOML
         echo "# Agent Team Instructions"
         echo ""
         echo "Agent-team specific protocols live in skills (orchestrate, conventions, worker-protocol, qa-checklist, message-schema, project)."
-        for rules_file in $(ls "$RULES_DIR"/*.md | sort); do
+        for rules_file in "$RULES_DIR"/*.md; do
             echo ""
             cat "$rules_file"
         done