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>

features/desktop/hyprland/config/monitors.conf

@@ -13,7 +13,7 @@
 # Straight 1x setup for low-resolution displays like 1080p or 1440p
 # Or for ultrawide monitors like 34" 3440x1440 or 49" 5120x1440
  env = GDK_SCALE,1
- monitor=,preferred,auto,1
+ monitor=,highres,auto,1
 
 # Portrait/rotated secondary monitor (transform: 1 = 90°, 3 = 270°)
 # monitor = DP-2, preferred, auto, 1, transform, 1