NixOS installer (flake + Lix)
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1) Build is prewired with Lix; the installer ISO includes the repo.
2) Run the guided Btrfs installer:

   sudo ./scripts/install-btrfs.sh

   - Interactive by default (choose disk, LUKS, swap).
   - Non-interactive example:
     sudo NON_INTERACTIVE=1 USE_LUKS=1 LUKS_PASSPHRASE='secret' SWAP_GB=4 DISK=/dev/sda HOSTNAME=myhost ./scripts/install-btrfs.sh

3) After install finishes, reboot into the new system.

Notes
- Filesystem is always Btrfs with subvolumes: root, home, nix (and swapfile if enabled).
- The flake lives under /etc/nixos on the target; edit hosts/<hostname>.nix to customize.