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/src/pages/Settings.tsx

@@ -0,0 +1,55 @@
+import { useEffect, useState } from "react";
+import { useToast } from "../toast";
+
+export default function Settings() {
+  const toast = useToast();
+  const [apiBase, setApiBase] = useState("");
+  const [light, setLight] = useState(false);
+
+  useEffect(() => {
+    setApiBase(localStorage.getItem("apiBase") || "");
+    setLight(document.documentElement.classList.contains("light"));
+  }, []);
+
+  const save = () => {
+    localStorage.setItem("apiBase", apiBase);
+    toast("Saved API base — reload for WS");
+  };
+
+  const toggleTheme = () => {
+    const next = !light;
+    setLight(next);
+    document.documentElement.classList.toggle("light", next);
+    document.documentElement.classList.toggle("dark", !next);
+    localStorage.setItem("theme", next ? "light" : "dark");
+    toast(next ? "Light" : "Dark");
+  };
+
+  return (
+    <div className="glass max-w-xl space-y-6 p-6">
+      <h1 className="font-display text-2xl font-bold">Settings</h1>
+      <label className="block text-sm">
+        API base (empty = same host)
+        <input
+          value={apiBase}
+          onChange={(e) => setApiBase(e.target.value)}
+          className="mt-1 w-full rounded-2xl border border-white/10 bg-black/25 px-4 py-2"
+          placeholder="http://192.168.4.1"
+        />
+      </label>
+      <button type="button" onClick={save} className="rounded-2xl bg-bubble-accent px-4 py-2 font-semibold">
+        Save
+      </button>
+      <div className="flex items-center justify-between rounded-2xl border border-white/10 bg-black/20 px-4 py-3">
+        <span className="text-sm">Theme</span>
+        <button type="button" onClick={toggleTheme} className="rounded-full border border-white/15 px-4 py-1 text-sm">
+          {light ? "Switch to dark" : "Switch to light"}
+        </button>
+      </div>
+      <p className="text-xs text-slate-500">
+        Firmware opens a <strong>password-free</strong> SoftAP named <strong>PN532-Toolkit</strong> (lab
+        default). mDNS: <code>pn532tool.local</code>
+      </p>
+    </div>
+  );
+}