Add a systemd timer that triggers builds for all hosts every 2 hours
via NATS, keeping the binary cache warm.
- Add scheduler.nix with timer (every 2h) and oneshot service
- Add scheduler NATS user to DEPLOY account
- Add Vault secret and variable for scheduler NKey
- Increase nix-cache02 memory from 16GB to 20GB
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
