Web UI login with the kiosk's PIN/password; shortcuts list on the Sites page

When the kiosk's password protection is on, the Web UI now asks for the same
PIN/password the lock screen uses: random session cookie (12 h, HttpOnly,
SameSite=Strict), the lock screen's wrong-code slowdown, sessions end when
the kiosk's code changes, sign out. With protection off nothing changes.
The Sites page (Web UI and terminal menu) lists the back/forward/home and
site-switching keys.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013wi3ZQveYdjfcrEsyazq32

menus/sites.sh

@@ -89,6 +89,8 @@ sites_status() {
     else
         echo "Auto-rotation: off (all pages manual/hidden)"
     fi
+    echo "Keys on the kiosk: Alt+Left back, Alt+Right forward, Alt+Home this page's own address,"
+    echo "                   Ctrl+Tab / Ctrl+PageDown next site, Ctrl+Shift+Tab / Ctrl+PageUp previous"
     if [[ "$HOME_TAB_INDEX" != "-1" ]]; then
         echo "Home page: #$((HOME_TAB_INDEX + 1)), ${INACTIVITY_TIMEOUT}s inactivity timeout"
     else