Wires beszel-agent into all tailscale-router variants (lxc/linode/proxmox)
by importing enable-agent.nix in the build type and host-token.nix in the
host file. Adds the sops creation rule for secrets/tailscale-router.yaml
(all three platform variants as recipients). The secrets file must be
created manually before deploying — see instructions in PR.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>