Folder image slideshow sites; Electron 42 -> 44

Slideshow: a site whose path is a local folder (/home/kiosk/photos/, or
any existing directory) plays its images full-screen instead of showing
Chromium's directory listing. kiosk-app/slideshow.js maps the folder URL
to slideshow.html (resolveSiteUrl - used where main.js loads a view and
where attachView re-checks the configured URL) and pushes the image list
into the page from the main process (the page has no fs access), re-read
every minute so added/removed images show up without a restart. Natural
file-name order, crossfade, letterboxed by default; optional
slideshow.json in the folder: interval, shuffle, fit, transition,
recursive. provision_install_app already copies kiosk-app/*.js/*.html,
so new installs and Advanced -> Upgrade pick it up.

Electron: ^42.0.0 -> ^44.0.0. Electron supports the latest three majors
(44/43/42), so 42 drops out when 45 ships. Checked the 43/44 breaking
changes against kiosk-app: nothing it uses changed (no clipboard,
safeStorage, net.request, utilityProcess; BrowserView is deprecated but
still present through 46). The offline bundle builder now retries
Electron's install.js download, which crashes outright if a large
download is cut off mid-stream.

Tested with the real main.js on Electron 44.5.1 under Xvfb + Openbox:
slideshow fills the screen, cycles in order (01, 02, 10) skipping a .txt
file, honours slideshow.json, and an image added mid-run joined the
rotation after the refresh. Offline bundle rebuilt with Electron 44.5.1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Cjz8a58eB5P9sUweqd3NHm

menus/sites.sh

@@ -136,6 +136,9 @@ action_add_page() {
     echo "    0  = manual only (swipe/nav menu to reach it)"
     echo "   -1  = hidden (PIN-gated, F10 or 3-finger swipe)"
     echo
+    echo "URL: a web address, or a path on this kiosk - a file (page, PDF,"
+    echo "image) like /home/kiosk/docs/menu.pdf, or a folder of images ending"
+    echo "in / like /home/kiosk/photos/ for a slideshow."
 
     local raw_url url dur name needs_auth user pass
     read -r -p "URL: " raw_url