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/main/board_rgb_off.h

@@ -0,0 +1,4 @@
+#pragma once
+
+/** One-shot: drive onboard WS2812/SK6812 to black, then release RMT. */
+void board_rgb_led_quiet(void);