fix(ui): NodeList.forEach not available on iOS 9 (Safari < 10)

NodeList.prototype.forEach was added in Safari 10 / iOS 10.
On iOS 9 it throws 'TypeError: forEach is not a function' at
init time, before connect() is called — leaving the app stuck
on 'Nicht verbunden' despite the async/await fix.

Added qsa(selector, root?) helper that wraps querySelectorAll
in Array.prototype.slice.call() to produce a real Array, then
replaced all three call sites:
  - document.querySelectorAll('.btn-seek').forEach
  - starEls (stored NodeList).forEach  x2
  - playlistList.querySelectorAll('li').forEach

Array.prototype.forEach has been safe since iOS 4.

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

web/static/app.js

@@ -29,6 +29,12 @@ function apiFetch(url, opts) {
 // String.prototype.padStart not available in iOS < 10.
 function pad2(n) { return n < 10 ? '0' + n : '' + n; }
 
+// NodeList.prototype.forEach not available in iOS < 10.
+// Wrap querySelectorAll results in a real Array before iterating.
+function qsa(selector, root) {
+  return Array.prototype.slice.call((root || document).querySelectorAll(selector));
+}
+
 // ── DOM refs ──────────────────────────────────────────────────────────────────
 var $ = function(id) { return document.getElementById(id); };
 
@@ -172,7 +178,7 @@ $('btn-stop').addEventListener('click', function() { send({ cmd: 'stop' }); });
 $('btn-next').addEventListener('click', function() { send({ cmd: 'next' }); });
 $('btn-prev').addEventListener('click', function() { send({ cmd: 'prev' }); });
 
-document.querySelectorAll('.btn-seek').forEach(function(btn) {
+qsa('.btn-seek').forEach(function(btn) {
   btn.addEventListener('click', function() {
     send({ cmd: 'seek', delta: parseInt(btn.dataset.delta, 10) });
   });
@@ -224,7 +230,7 @@ function updateMuteBtn(muted) {
 }
 
 // ── Rating (stars) ────────────────────────────────────────────────────────────
-var starEls = document.querySelectorAll('.star');
+var starEls = qsa('.star');
 
 function fetchRating() {
   apiFetch('/api/rating')
@@ -509,7 +515,7 @@ function openPlaylist() {
 
 function updatePlaylistHighlight() {
   if (playlistOverlay.classList.contains('hidden')) return;
-  playlistList.querySelectorAll('li').forEach(function(li) {
+  qsa('li', playlistList).forEach(function(li) {
     var isCurrent = parseInt(li.dataset.index, 10) === currentPlaylistPos - 1;
     li.classList.toggle('current', isCurrent);
   });