ci: GitLab-Pipeline - build_embedded + manueller npm-Publish nach rohana (threadnet-call#1)

Registry-Entscheidung evidenzbasiert: das Package ist pnpm-Dependency von
ThreadNet-Webs apps/web, der Lockfile pinnt die Tarball-URL auf rohana -
Registry bleibt dort. Publish-Auth ueber CI-Variable GITEA_NPM_TOKEN statt
lokaler Klartext-.npmrc.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/useBehavior.ts

@@ -0,0 +1,25 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { useCallback, useSyncExternalStore } from "react";
+
+import { type Behavior } from "./state/Behavior";
+
+/**
+ * React hook which reactively reads the value of a behavior.
+ */
+export function useBehavior<T>(behavior: Behavior<T>): T {
+  const subscribe = useCallback(
+    (onChange: () => void) => {
+      const s = behavior.subscribe(onChange);
+      return (): void => s.unsubscribe();
+    },
+    [behavior],
+  );
+  const getValue = useCallback(() => behavior.value, [behavior]);
+  return useSyncExternalStore(subscribe, getValue);
+}