Install NixOS

The final phase builds and installs NixOS from the per-host repo that setup host generated, sets your passwords, and makes the machine reachable after reboot.

Run it from the menu, or directly:

setup install

It auto-discovers the host repo and reads the host name from its flake, then shows a review screen:

================ Review =================
Host repo:     /mnt/home/ryan/nixos
Host:          box
User:          ryan
Target root:   /mnt
=========================================

This builds and installs NixOS into /mnt (downloads the system
    closure from the binary cache) and sets passwords.

? Proceed with install? (Y/n)

After you confirm, it:

1. Re-pins sway-home to its latest commit (so a fresh fix is picked up without regenerating the repo) and commits the updated lock. Pass --no-update to install from the committed pin instead.
2. Runs nixos-install, which downloads and builds the system and, at the end, prompts you to set the root password.
3. Sets a password for your user account.
4. Fixes ownership of the config repo so it belongs to your user after reboot.
5. Copies the live ISO’s NetworkManager profiles (e.g. your pre-seeded WiFi) into the target, so a headless machine stays reachable.
6. Copies the live ISO’s SSH host keys into the target, so the installed machine keeps the same SSH identity – no “REMOTE HOST IDENTIFICATION HAS CHANGED” warning for anyone who already trusted the live host key.

✅ Install complete.
   Config repo: /home/ryan/nixos  (owned by ryan after reboot)
   Apply future changes with:  sudo nixos-rebuild switch --flake .#box

? Reboot now? (y/N)