fix(install): survive the live ISO offline and its non-interactive bash

Found by running the unattended install in an offline QEMU VM:
- compgen is missing from nixpkgs' non-interactive bash (the package
  shebang) — replaced with plain glob tests in hardware-db and prewipe
- disko's eval resolves <nixpkgs> via NIX_PATH (a dead channel on the
  ISO) and tried channels.nixos.org — export NIX_PATH to the pinned
  nixpkgs source and point the flake registry at an empty baked file
- lock nomarchy by path (the source the ISO carries) instead of
  git+https: git inputs clone even when narHash is known, which kills
  offline installs; `original` keeps the forge URL so a later
  `nix flake update` re-resolves normally. Works from dirty-tree ISOs too.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkgs/nomarchy-install/hardware-db.sh

@@ -140,8 +140,10 @@ nomarchy_detect_hw() {
         (( intelgpu )) && { echo "MODULE common-gpu-intel";  echo "DETAIL gpu: Intel";  detected=1; }
     fi
 
-    # Chassis
-    if compgen -G "/sys/class/power_supply/BAT*" >/dev/null; then
+    # Chassis (glob test, not compgen — nixpkgs' non-interactive bash
+    # is built without the completion builtins)
+    local bats=(/sys/class/power_supply/BAT*)
+    if [[ -e "${bats[0]}" ]]; then
         echo "MODULE common-pc-laptop"
         echo "DETAIL chassis: laptop (battery present)"
     else