add ylw user to xlab-gateway

xlab-gateway: add hardware-configuration.nix, disable wait-online ...

- Import generated hardware-configuration.nix (Intel CPU microcode,
  boot modules for ehci_pci, ahci, nvme, kvm-intel)
- Disable systemd-networkd-wait-online (gateway doesn't need to block
  boot waiting for WireGuard interfaces)

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Initial skyworks infrastructure flake ...

Unified NixOS configuration for skydick (storage server) and
xlab-gateway (lab router). Flat module structure with shared
common/users/ssh modules, agenix secrets, disko, and deploy-rs.

Co-Authored-By: Claude Opus 4.6 <[email protected]>