fix(ui): iOS 9 emoji fallback -- use ASCII symbols where glyphs are missing

Media-control emoji (U+23EE U+23F8 U+23F9 U+23ED) and 🔊 🔇 📋 🚫
are absent from the iOS 9 system font and render as empty boxes on iPad 2.

Added isLegacyIOS detection (iOS <= 9 via UA) and a SYM symbol table
that picks between emoji (modern) and plain-text fallbacks for iOS 9:
  prev=<< pause=|| stop=■ next=>> volOn=vol volOff=mut playlist=PL skip=✕

Static buttons replaced at boot; dynamic updates (play/pause, mute)
use SYM throughout. Modern browsers completely unaffected.

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

web/static/app.js

@@ -29,6 +29,36 @@ function apiFetch(url, opts) {
 // String.prototype.padStart not available in iOS < 10.
 function pad2(n) { return n < 10 ? '0' + n : '' + n; }
 
+// iOS version detection — used to pick emoji vs. ASCII symbols.
+// Media-control emoji (⏮ ⏸ ⏹ ⏭) and several other glyphs are absent on iOS 9.
+var isLegacyIOS = (function() {
+  var m = navigator.userAgent.match(/OS (\d+)_/);
+  return /iPad|iPhone/.test(navigator.userAgent) && m && parseInt(m[1], 10) <= 9;
+}());
+
+// Symbol set: modern emoji for capable browsers, plain text for iOS ≤ 9.
+var SYM = isLegacyIOS ? {
+  prev:    '<<',
+  play:    '▶',   // U+25B6 — works on iOS 9
+  pause:   '||',
+  stop:    '■',   // U+25A0 — works on iOS 9
+  next:    '>>',
+  volOn:   'vol',
+  volOff:  'mut',
+  playlist:'PL',
+  skip:    '✕'    // U+2715 — works on iOS 9
+} : {
+  prev:    '⏮',
+  play:    '▶',
+  pause:   '⏸',
+  stop:    '⏹',
+  next:    '⏭',
+  volOn:   '🔊',
+  volOff:  '🔇',
+  playlist:'📋',
+  skip:    '🚫'
+};
+
 // NodeList.prototype.forEach not available in iOS < 10.
 // Wrap querySelectorAll results in a real Array before iterating.
 function qsa(selector, root) {
@@ -158,7 +188,7 @@ function applyStatus(st) {
     timeLength.textContent   = '-0:00';
   }
 
-  btnPlay.textContent = st.state === 'playing' ? '⏸' : '▶';
+  btnPlay.textContent = st.state === 'playing' ? SYM.pause : SYM.play;
   winampPlaying = st.state === 'playing';
 
   if (typeof st.volume === 'number') {
@@ -170,7 +200,7 @@ function applyStatus(st) {
 
 // ── Controls ──────────────────────────────────────────────────────────────────
 btnPlay.addEventListener('click', function() {
-  var playing = btnPlay.textContent === '⏸';
+  var playing = btnPlay.textContent === SYM.pause;
   send({ cmd: playing ? 'pause' : 'play' });
 });
 
@@ -225,7 +255,7 @@ function updateVolumeFill(muted) {
   volumeFill.classList.toggle('muted', muted);
 }
 function updateMuteBtn(muted) {
-  btnMute.textContent = muted ? '🔇' : '🔊';
+  btnMute.textContent = muted ? SYM.volOff : SYM.volOn;
   btnMute.classList.toggle('muted', muted);
 }
 
@@ -528,5 +558,17 @@ function scrollToCurrentTrack() {
 }
 
 // ── Boot ──────────────────────────────────────────────────────────────────────
+
+// Replace emoji with legacy symbols on iOS 9 where the glyphs are missing.
+if (isLegacyIOS) {
+  $('btn-prev').textContent         = SYM.prev;
+  $('btn-play').textContent         = SYM.play;
+  $('btn-stop').textContent         = SYM.stop;
+  $('btn-next').textContent         = SYM.next;
+  $('btn-mute').textContent         = SYM.volOn;
+  $('btn-show-playlist').textContent = SYM.playlist;
+  $('btn-kill').textContent         = SYM.skip + ' Überspringen';
+}
+
 connect();
 renderFrame();