fix: use generic 'kiosk' username, prompt only for senior's name

Removes the username prompt — all installs use 'kiosk' as the system
user. Only the senior's display name is asked during first-boot setup.

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

install-kiosk.sh

@@ -14,21 +14,15 @@ echo "============================================"
 echo
 
 # ── Prompt for user details ────────────────────────────────────────
-while true; do
-  read -rp "Enter a username for this kiosk (e.g. mary): " KIOSK_USER
-  KIOSK_USER=$(echo "$KIOSK_USER" | tr '[:upper:]' '[:lower:]' | tr -cd 'a-z0-9_-')
-  if [ -n "$KIOSK_USER" ]; then break; fi
-  echo "  Invalid — use only letters, numbers, hyphens, underscores."
-done
+KIOSK_USER="kiosk"
 
 while true; do
-  read -rp "Enter the senior's display name   (e.g. Mary Smith): " KIOSK_NAME
+  read -rp "Enter the senior's name (e.g. Mary Smith): " KIOSK_NAME
   if [ -n "$KIOSK_NAME" ]; then break; fi
   echo "  Name cannot be empty."
 done
 
 echo
-echo "  Username : $KIOSK_USER"
 echo "  Name     : $KIOSK_NAME"
 echo
 read -rp "Proceed with setup? [Y/n] " CONFIRM