Add real first-time provisioning to install.sh (v2.14.0)

Until now ./install.sh only managed an already-installed kiosk;
ubuntu-based-kiosk.sh was still the only path from a bare Ubuntu Server
box to a running one. install.sh now provisions from scratch too:
packages, kiosk user, Node.js/Electron, LightDM+Openbox autologin,
audio/video/HDMI/power-button hardware setup, and the firewall, then
hands off to the already-migrated Core Settings/Advanced menus for
initial configuration instead of reimplementing that logic again.

- lib/provision.sh: the new provisioning flow, built mostly by calling
  existing menus (core_settings_menu, emergency hotspot, virtual
  consoles) - cuts it to ~300 lines against the legacy script's
  ~4,000-line first_time_install().
- lib/electron.sh: electron_install_binary() extracted out of
  menus/advanced_electron.sh so provisioning and the existing "Fix
  blank screen" action share one implementation.
- kiosk-app/ and provision/files/: the Electron app source and every
  system template file, extracted byte-for-byte out of
  ubuntu-based-kiosk.sh's heredocs into real files.
- Found and fixed a bash set -e gotcha along the way: testing a
  multi-statement function as an if-condition (`if ! some_func; then`)
  silently exempts everything inside that function from set -e for the
  duration of the call. Fixed in the new provisioning code and in
  menus/advanced_electron.sh's pre-existing repair action, which had
  the same shape.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VfsFSoRqfbRG7XAg5RoE7e

provision/files/usr/local/bin/kiosk-power-button.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+# Power button handler - sends SIGUSR1 to Electron to show power menu
+# This runs as ROOT from acpid, so it can signal any process
+
+logger "KIOSK POWER: Button pressed"
+
+# Find the Electron main process (runs as kiosk user)
+PIDS=$(pgrep -u kiosk -f "electron" 2>/dev/null)
+
+if [ -z "$PIDS" ]; then
+    logger "KIOSK POWER: No Electron process found"
+    exit 1
+fi
+
+# Send SIGUSR1 to all Electron processes (the main one will handle it)
+for PID in $PIDS; do
+    logger "KIOSK POWER: Sending SIGUSR1 to PID $PID"
+    kill -USR1 $PID 2>/dev/null
+done
+
+logger "KIOSK POWER: Signal sent"