fix: speed controls local playbackRate only, TTS generation always uses speed 1

Speed buttons now set audio.playbackRate directly (on load and on change)
instead of passing the speed to Kokoro. The TTS generation request always
sends speed:1 so the cached audio is at normal pitch/tempo and the browser
handles tempo adjustment locally.

scraper/internal/server/ui.go

@@ -2704,6 +2704,7 @@ const chapterTmpl = `
       b.classList.toggle('text-zinc-300',    !active);
     });
     try { localStorage.setItem(LS_SPEED, btn.dataset.speed); } catch(_) {}
+    if (audio.src) audio.playbackRate = parseFloat(btn.dataset.speed);
   }
   window.selectSpeed = selectSpeed;
   (function loadSettings() {
@@ -2841,7 +2842,7 @@ const chapterTmpl = `
     fetch('/ui/audio/' + SLUG + '/' + chapterN, {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
-      body: JSON.stringify({ voice: voiceSel.value, speed: getSpeed() }),
+      body: JSON.stringify({ voice: voiceSel.value, speed: 1 }),
       signal: ctrl.signal
     })
     .then(function (res) {
@@ -2928,6 +2929,7 @@ const chapterTmpl = `
       if (stale()) return;
       if (autoplay) audio.autoplay = true;
       audio.src = url; audio.load();
+      audio.playbackRate = getSpeed();
       registerMediaSession();
     });
   }