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

web/postcss.config.js

@@ -0,0 +1,6 @@
+export default {
+  plugins: {
+    tailwindcss: {},
+    autoprefixer: {},
+  },
+};