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/api.ts

@@ -0,0 +1,62 @@
+/** Stored API origin; trailing slashes stripped so paths join cleanly. */
+export function apiBaseUrl(): string {
+  return (localStorage.getItem("apiBase") || "").replace(/\/+$/, "");
+}
+
+export function apiUrl(path: string): string {
+  const b = apiBaseUrl();
+  const p = path.startsWith("/") ? path : `/${path}`;
+  return b ? `${b}${p}` : p;
+}
+
+export async function apiGet<T>(path: string): Promise<T> {
+  const r = await fetch(apiUrl(path));
+  if (!r.ok) {
+    throw new Error(await r.text());
+  }
+  return r.json() as Promise<T>;
+}
+
+export async function apiPost<T>(path: string, body: unknown): Promise<T> {
+  const r = await fetch(apiUrl(path), {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(body),
+  });
+  if (!r.ok) {
+    throw new Error(await r.text());
+  }
+  return r.json() as Promise<T>;
+}
+
+export type SessionInfo = {
+  usedBytes: number;
+  maxBytes: number;
+  lines: number;
+  full: boolean;
+  deepCapture: boolean;
+};
+
+export type Status = {
+  app: string;
+  uptimeMs: number;
+  freeHeap: number;
+  wifiMode: number;
+  pn532?: { ic: number; fwHi: number; fwLo: number };
+  scanning: boolean;
+  session?: SessionInfo;
+};
+
+export type Tag = {
+  uid: string;
+  uidLen: number;
+  atqa: number;
+  sak: number;
+  typeHint: number;
+  /** ATQA as 4 hex digits (MSB first, same as firmware). */
+  atqaHex?: string;
+  sakHex?: string;
+  typeGuess?: string;
+  /** PN532 `GetGeneralStatus` payload bytes (chip-dependent length). */
+  pn532GeneralStatus?: number[];
+};