fix(installer): unblock disko, bootloader, HM activation, hyprland res

- Pass --yes-wipe-all-disks to disko so the silent gum-spin path no
  longer hangs forever waiting on a hidden "yes" confirmation prompt
  (added in disko 1.13's destroy,format,mount mode).
- Stop threading an externally-built pkgs into the user flake's
  nixosSystem; configure nixpkgs through the module system instead so
  core/system/default.nix's nixpkgs.config.allowUnfree stops conflicting
  with the assertion "system configures nixpkgs with an externally
  created instance".
- Enable boot.loader.systemd-boot in the generated system.nix so the
  installed system has an actual bootloader (disko already lays out a
  1 GiB ESP at /boot).
- Bump nix.settings.download-buffer-size to 512 MiB to silence the
  "download buffer is full" warning on large NAR fetches.
- Activate home-manager via `runuser -l` instead of `runuser -u … --
  env HOME=…`. The latter only switches uid and leaves \$USER=root, so
  HM's activation script saw root, warned, and wrote dotfiles into
  /root/ — meaning the user's first login had no Hyprland config.
- Revert default Hyprland monitor line back to highres (live ISO and
  user default) — preferred falls back to EDID's 1024x768 in QEMU and
  on several laptop panels, which is the bug highres was put there to
  defeat.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

flake.nix

@@ -168,10 +168,10 @@
               # Live-ISO-only welcome. Pops a notification a few seconds
               # after the graphical session is up and opens a terminal
               # parked at the installer command, so the user never has to
-              # hunt for it. Force preferred monitor detection as some
+              # hunt for it. Force highres monitor detection as some
               # hardware defaults to 1024x768.
               wayland.windowManager.hyprland.extraConfig = nixpkgs.lib.mkAfter ''
-                monitor = , preferred, auto, 1
+                monitor = , highres, auto, 1
                 exec-once = sh -c 'sleep 3; notify-send -u critical -t 0 "Welcome to Nomarchy" "Run \`sudo /etc/install.sh\` in the open terminal — or \`--dry-run\` to preview."'
 
                 exec-once = sh -c 'sleep 4; alacritty --title "Nomarchy Installer" -e bash -lc "echo; echo \"Welcome to the Nomarchy live ISO.\"; echo; echo \"  sudo /etc/install.sh           # install\"; echo \"  sudo /etc/install.sh --dry-run # preview only\"; echo \"  sudo /etc/install.sh --resume  # resume after an interrupt\"; echo; exec bash"'