feat(deploy): add NixOS live USB ISO for ATM hardware testing

Add NixOS configuration to build a bootable live USB ISO that runs the
ATM Electron app in kiosk mode on physical hardware (UpBoard). The ISO
boots from squashfs, auto-starts X11/openbox, and launches Electron in
production mode.

Key changes:
- deploy/nixos/live.nix: Live USB module (squashfs+tmpfs, no disk install)
- deploy/nixos/flake.nix: Nix flake with ISO build output
- deploy/nixos/provision-atm.sh: Auto-provision LP credentials via API
- deploy/nixos/build-iso.sh: End-to-end build workflow script
- apps/machine: Fix Electron production mode (ELECTRON_FORCE_PROD),
  Vue Router hash mode for file:// protocol, relative asset paths

Build: cd deploy/nixos && bash build-iso.sh
Test:  qemu-system-x86_64 -enable-kvm -m 2G -cdrom result/iso/*.iso

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/machine/electron/main.ts

@@ -40,7 +40,9 @@ function loadEnvFile() {
 loadEnvFile()
 
 // Determine if we're in development
-const isDev = process.env.NODE_ENV === 'development' || !app.isPackaged
+const isDev =
+  process.env.ELECTRON_FORCE_PROD !== '1' &&
+  (process.env.NODE_ENV === 'development' || !app.isPackaged)
 
 // Window dimensions (vertical ATM display)
 const WINDOW_WIDTH = 1080