feat: add stagger() and vibrate() UX utilities with tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test-ux-utils.js

@@ -0,0 +1,49 @@
+/**
+ * Tests: UX Utilities (stagger, vibrate)
+ * Läuft im Node-Kontext — kein DOM verfügbar, daher nur Pure-Logic-Tests.
+ */
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+
+// Minimales Window/Navigator-Mock für Node
+const { stagger, vibrate } = await (async () => {
+  // stagger braucht window.matchMedia — wir mocken es
+  global.window = {
+    matchMedia: () => ({ matches: false }),
+  };
+  // navigator ist in Node ein getter-only property — über defineProperty überschreiben
+  Object.defineProperty(global, 'navigator', {
+    value: { vibrate: null },
+    writable: true,
+    configurable: true,
+  });
+  return import('./public/utils/ux.js');
+})();
+
+test('stagger: setzt opacity:0 auf alle Elemente', () => {
+  const els = [{ style: {} }, { style: {} }, { style: {} }];
+  stagger(els, { delay: 0, duration: 0 });
+  assert.equal(els[0].style.opacity, '0');
+  assert.equal(els[1].style.opacity, '0');
+  assert.equal(els[2].style.opacity, '0');
+});
+
+test('stagger: tut nichts bei prefers-reduced-motion', () => {
+  global.window.matchMedia = () => ({ matches: true });
+  const els = [{ style: {} }];
+  stagger(els);
+  assert.equal(els[0].style.opacity, undefined); // unverändert
+  global.window.matchMedia = () => ({ matches: false }); // reset
+});
+
+test('vibrate: tut nichts wenn API nicht vorhanden', () => {
+  Object.defineProperty(global, 'navigator', { value: { vibrate: null }, writable: true, configurable: true });
+  assert.doesNotThrow(() => vibrate(10));
+});
+
+test('vibrate: ruft navigator.vibrate auf wenn vorhanden', () => {
+  let called = null;
+  Object.defineProperty(global, 'navigator', { value: { vibrate: (p) => { called = p; } }, writable: true, configurable: true });
+  vibrate(15);
+  assert.equal(called, 15);
+});