chore: add playground serve script

playground/serve.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+# Serve the NISPS playground, finding an open port if needed.
+
+PORT="${1:-8000}"
+MAX_ATTEMPTS=20
+DIR="$(cd "$(dirname "$0")" && pwd)"
+
+for ((i = 0; i < MAX_ATTEMPTS; i++)); do
+  candidate=$((PORT + i))
+  if ! ss -tlnp 2>/dev/null | grep -q ":${candidate} "; then
+    echo "Serving playground at http://localhost:${candidate}"
+    exec python3 -m http.server "$candidate" -d "$DIR"
+  fi
+  echo "Port ${candidate} in use, trying next..."
+done
+
+echo "No open port found in range ${PORT}–$((PORT + MAX_ATTEMPTS - 1))" >&2
+exit 1