fix: use audio.autoplay flag to unblock autoplay policy on chapter auto-advance

When the auto-next feature navigated to a new chapter and startAudio was
called on page load (outside a user gesture), the browser's autoplay policy
blocked the audio.play() call inside onCanPlay. Fix by setting
audio.autoplay = true before audio.load() when started automatically, then
resetting it in onCanPlay so manual pause/play is unaffected.

scraper/internal/server/ui.go

@@ -2871,7 +2871,7 @@ const chapterTmpl = `
     if (!activePara || activePara !== paras[idx]) highlightPara(idx);
   }
 
-  function onCanPlay()    { if (stale()) { audio.removeEventListener('canplay', onCanPlay); return; } if (audio.paused) audio.play().then(setPlaying).catch(function(e){ setError(e.message); }); }
+  function onCanPlay()    { if (stale()) { audio.removeEventListener('canplay', onCanPlay); return; } audio.autoplay = false; if (audio.paused) audio.play().then(setPlaying).catch(function(e){ setError(e.message); }); }
   function onWaiting()    { if (!stale()) setStatus('Buffering\u2026'); }
   function onPlaying()    { if (!stale()) setPlaying(); }
   function onPause()      { if (!stale() && !audio.ended) setPaused(); }
@@ -2921,11 +2921,12 @@ const chapterTmpl = `
     navigator.mediaSession.setActionHandler('seekto', function(d) { if (isFinite(d.seekTime)) { audio.currentTime = d.seekTime; updateSeek(); } });
   }
 
-  function startAudio() {
+  function startAudio(autoplay) {
     setGenerating();
     highlightPara(0);
     generateAudio(CHAPTER_N, function (url) {
       if (stale()) return;
+      if (autoplay) audio.autoplay = true;
       audio.src = url; audio.load();
       registerMediaSession();
     });
@@ -2948,10 +2949,10 @@ const chapterTmpl = `
   if (_autostart) {
     try { localStorage.removeItem('tts_autostart'); } catch(_) {}
     autoplayChk.checked = true;
-    setTimeout(startAudio, 100);
+    setTimeout(function() { startAudio(true); }, 100);
   } else if (new URLSearchParams(window.location.search).get('autoplay') === '1') {
     autoplayChk.checked = true;
-    setTimeout(startAudio, 100);
+    setTimeout(function() { startAudio(true); }, 100);
   }
 
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