Add PN532 toolkit firmware, web UI, and embedded SPIFFS assets

Includes ESP-IDF NFC stack (deep capture, 4K Classic geometry, UL write API,
open SoftAP), React dashboard with live tag diagnostics, and docs. README
updated for APIs and lab Wi-Fi defaults.

Made-with: Cursor

firmware/flash.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+# Flash PN532 toolkit. Requires ESP-IDF 5.x in PATH (run export.sh first).
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")" && pwd)"
+PORT="${ESPPORT:-${1:-/dev/cu.usbserial-A5069RR4}}"
+cd "$ROOT"
+if ! command -v idf.py >/dev/null 2>&1; then
+  echo "idf.py not found. Source your ESP-IDF export.sh, then re-run:" >&2
+  echo "  ESPPORT=$PORT $0" >&2
+  exit 1
+fi
+idf.py -p "$PORT" flash