fix(installer): replace confirmation prompt with 5-second countdown

curl | bash pipes stdin so read gets EOF and returns non-zero, which
set -euo pipefail treats as an error and aborts immediately. Replaced
the interactive prompt with a sleep 5 countdown — works whether the
script is piped or run directly.

Bumps version to 0.6.3.

scripts/install.sh

@@ -95,9 +95,8 @@ echo "  Admin username    : $ADMIN_USER"
 echo "  Admin email       : $ADMIN_EMAIL"
 echo "  Admin password    : $([ "$GENERATED_PASS" = "true" ] && echo "<auto-generated>" || echo "$ADMIN_PASS")"
 echo ""
-read -r -p "Continue? [Y/n] " CONFIRM < /dev/tty || CONFIRM="Y"
-CONFIRM="${CONFIRM:-Y}"
-[[ "$CONFIRM" =~ ^[Yy]$ ]] || { echo "Aborted."; exit 0; }
+echo "  Starting in 5 seconds — press Ctrl+C to abort."
+sleep 5
 
 # ── Logging ───────────────────────────────────────────────────────────────────
 mkdir -p /var/log/nixpanel