Add kiosk desktop app

Tauri app for the Pi. Media runs through the native LiveKit SDK because
WebKitGTK has no WebRTC, with frames encoded in Rust and drawn to a canvas
under the annotation overlay.

apps/kiosk-client/src/lib/api.ts

@@ -0,0 +1,86 @@
+import type { KioskLayout, KioskPinResponse, KioskSessionResponse } from "@pistation/shared-types";
+
+export interface RegisterResult {
+  kioskId: string;
+  kioskToken: string;
+  roomName: string;
+  livekitUrl: string;
+  rotationSeconds: number;
+}
+
+export class KioskApiError extends Error {
+  readonly status: number;
+
+  constructor(status: number, message: string) {
+    super(message);
+    this.status = status;
+  }
+}
+
+async function request<T>(
+  serverUrl: string,
+  path: string,
+  options: { method?: string; token?: string; body?: unknown } = {}
+): Promise<T> {
+  const headers: Record<string, string> = {};
+  if (options.body !== undefined) headers["content-type"] = "application/json";
+  if (options.token) headers["authorization"] = `Bearer ${options.token}`;
+
+  let response: Response;
+
+  try {
+    response = await fetch(`${serverUrl.replace(/\/$/, "")}${path}`, {
+      method: options.method ?? "GET",
+      headers,
+      body: options.body === undefined ? undefined : JSON.stringify(options.body)
+    });
+  } catch {
+    throw new KioskApiError(0, `could not reach the server at ${serverUrl}`);
+  }
+
+  if (response.status === 204) return undefined as T;
+
+  const payload = await response.json().catch(() => null);
+
+  if (!response.ok) {
+    const message = (payload as { message?: string })?.message ?? `request failed: ${path}`;
+    throw new KioskApiError(response.status, message);
+  }
+
+  return payload as T;
+}
+
+export function registerKiosk(
+  serverUrl: string,
+  enrollmentToken: string,
+  hardwareId: string
+): Promise<RegisterResult> {
+  return request<RegisterResult>(serverUrl, "/api/kiosk/register", {
+    method: "POST",
+    body: { enrollmentToken, hardwareId }
+  });
+}
+
+export function fetchPin(serverUrl: string, token: string): Promise<KioskPinResponse> {
+  return request<KioskPinResponse>(serverUrl, "/api/kiosk/pin", { token });
+}
+
+export function fetchSession(serverUrl: string, token: string): Promise<KioskSessionResponse> {
+  return request<KioskSessionResponse>(serverUrl, "/api/kiosk/session", { token });
+}
+
+export function fetchLayout(serverUrl: string, token: string): Promise<KioskLayout> {
+  return request<KioskLayout>(serverUrl, "/api/kiosk/layout", { token });
+}
+
+export function sendHeartbeat(
+  serverUrl: string,
+  token: string,
+  metrics: unknown
+): Promise<void> {
+  return request<void>(serverUrl, "/api/kiosk/heartbeat", {
+    method: "POST",
+    token,
+    body: { metrics }
+  });
+}