Add codex environment scripts, README and AGENTS

AGENTS.md

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+# AGENTS.md
+
+## Repo purpose
+
+This repository contains flake-based NixOS configurations for Wayne’s LAN servers and workstation.
+
+The flake currently exposes these NixOS configurations:
+
+- `nixos`
+- `docker`
+- `kuma`
+- `server`
+- `nix-cache`
+- `nix-minimal`
+
+Do not deploy, switch, reboot, repartition, format disks, or run destructive install commands from this repository unless explicitly asked.
+
+## Safety rules
+
+- Never run `nixos-rebuild switch`, `boot`, `test`, `nixos-install`, `parted`, `mkfs`, `mkswap`, `swapon`, `mount`, or destructive disk commands in Codex.
+- Validation work should be limited to evaluation, linting, formatting checks, and `nix build --dry-run --no-link`.
+- Do not add secrets, tokens, private keys, password hashes, or live credentials to the repo.
+- Treat `flake.nix`, Home Manager config, and Nix config files as public.
+- If you find committed tokens or hashes, flag them immediately and recommend rotation/removal.
+
+## Expected commands
+
+Use these commands when validating changes:
+
+```bash
+bash scripts/codex-setup.sh
+bash scripts/codex-maintenance.sh
+bash scripts/codex-maintenance.sh dry-run