Add cookie-banner React example app

Interactive playground with themed banner, headless components,
and debug tabs demonstrating programmatic consent access via
getConsent() across separate bundles.

Signed-off-by: Émile Ré <emile@probo.com>

examples/cookie-banner-react/src/hooks/useConfig.ts

@@ -0,0 +1,47 @@
+import { useCallback, useSyncExternalStore } from "react";
+
+export interface Config {
+  bannerId: string;
+  baseUrl: string;
+}
+
+const STORAGE_KEY = "probo-example-config";
+
+const defaultConfig: Config = {
+  bannerId: "",
+  baseUrl: "",
+};
+
+function getSnapshot(): Config {
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    if (raw) return JSON.parse(raw) as Config;
+  } catch {
+    // ignore
+  }
+  return defaultConfig;
+}
+
+let cached = getSnapshot();
+const listeners = new Set<() => void>();
+
+function subscribe(cb: () => void): () => void {
+  listeners.add(cb);
+  return () => listeners.delete(cb);
+}
+
+function snapshot(): Config {
+  return cached;
+}
+
+function persist(next: Config): void {
+  cached = next;
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
+  for (const cb of listeners) cb();
+}
+
+export function useConfig(): [Config, (next: Config) => void] {
+  const config = useSyncExternalStore(subscribe, snapshot);
+  const setConfig = useCallback((next: Config) => persist(next), []);
+  return [config, setConfig];
+}