Hash the hidden-sites PIN and slow down repeated wrong PINs

.jitsi-pin now holds "sha256:<hex>" (or NOPIN) instead of the digits.
The menu writes the hashed form. A plain-digits file still works and
is converted by the kiosk app at startup.

The PIN is now checked in the main process instead of the PIN pad's
renderer, using the lock screen's slowdown, now factored out
(createCodeThrottle): 5 wrong in a row refuse entry for 30s, doubling
up to 5 minutes. The F10 PIN pad and the WiFi screen share one count.
The WiFi screen's close-after-5-tries is replaced by this. The PIN pad
no longer shows the default PIN on screen, and the menu no longer
echoes the PIN as it's typed.

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

menus/hidden_pin.sh

@@ -6,6 +6,12 @@
 # flat PIN file rather than config.json - a fourth shape for the framework
 # to prove out (plain file, not JSON at all).
 #
+# The file holds "NOPIN", or "sha256:<hex>" - the PIN is never stored as
+# plain digits (a file from before that is converted by the kiosk app at
+# startup; plain digits are still accepted until then). No file = the
+# default PIN 1234. The kiosk app reads it on every check, so changes
+# apply immediately, and slows down repeated wrong guesses.
+#
 # Depends on: lib/menu.sh, lib/config.sh being sourced first.
 ################################################################################
 
@@ -22,8 +28,10 @@ hidden_pin_status() {
         current_pin=$(sudo -u "$KIOSK_USER" cat "$pin_file" 2>/dev/null)
         if [[ "$current_pin" == "NOPIN" ]]; then
             echo "Current: no PIN (hidden pages open to anyone)"
+        elif [[ "$current_pin" == "sha256:$(hidden_pin_hash 1234)" || "$current_pin" == "1234" ]]; then
+            echo "Current: default PIN (1234) - set your own"
         else
-            echo "Current: PIN set (${#current_pin} digits)"
+            echo "Current: PIN set"
         fi
     else
         echo "Current: not configured (default: 1234)"
@@ -43,29 +51,36 @@ hidden_pin_menu() {
 # Actions
 ################################################################################
 
+hidden_pin_hash() {
+    echo -n "$1" | sha256sum | cut -d' ' -f1
+}
+
+# write_pin VALUE - VALUE is "NOPIN" or the PIN digits (stored hashed).
 write_pin() {
     local value="$1"
     local pin_file
     pin_file=$(hidden_pin_file)
 
+    [[ "$value" == "NOPIN" ]] || value="sha256:$(hidden_pin_hash "$value")"
     sudo mkdir -p "$KIOSK_DIR"
     echo "$value" | sudo -u "$KIOSK_USER" tee "$pin_file" > /dev/null
     sudo -u "$KIOSK_USER" chmod 600 "$pin_file"
-    log_warning "Restart the kiosk display for this to take effect"
 }
 
 action_set_pin() {
     echo
     local new_pin confirm_pin
     while true; do
-        read -r -p "Enter new PIN (4-8 digits): " new_pin
+        read -r -s -p "Enter new PIN (4-8 digits): " new_pin
+        echo
 
         if [[ ! "$new_pin" =~ ^[0-9]{4,8}$ ]]; then
             echo "❌ PIN must be 4-8 digits"
             continue
         fi
 
-        read -r -p "Confirm PIN: " confirm_pin
+        read -r -s -p "Confirm PIN: " confirm_pin
+        echo
 
         if [[ "$new_pin" == "$confirm_pin" ]]; then
             write_pin "$new_pin"