feat: persist TTS speed, voice, and auto-next in localStorage

Settings are loaded on page init and saved on every change so they carry
over across chapter navigation and page reloads.

scraper/internal/server/ui.go

@@ -718,10 +718,44 @@ const chapterTmpl = `
   var prefetchAbort  = null;
   var prefetchReady  = false; // true once canplay fired on prefetchAudio
 
+  // ── localStorage persistence ─────────────────────────────────────────────────
+  // Settings saved: tts_speed, tts_voice, tts_autonext
+  // Loaded once on page init; written on every change.
+
+  var LS_SPEED   = 'tts_speed';
+  var LS_VOICE   = 'tts_voice';
+  var LS_AUTONEXT = 'tts_autonext';
+
+  (function loadSettings() {
+    var savedSpeed = localStorage.getItem(LS_SPEED);
+    if (savedSpeed !== null) {
+      speedSlider.value = savedSpeed;
+      speedLabel.textContent = parseFloat(savedSpeed).toFixed(1) + '\u00D7';
+    }
+    var savedVoice = localStorage.getItem(LS_VOICE);
+    if (savedVoice !== null) {
+      var opt = voiceSel.querySelector('option[value="' + savedVoice + '"]');
+      if (opt) voiceSel.value = savedVoice;
+    }
+    var savedAutoNext = localStorage.getItem(LS_AUTONEXT);
+    if (savedAutoNext !== null) {
+      autoplayChk.checked = savedAutoNext === 'true';
+    }
+  })();
+
   // ── speed slider ─────────────────────────────────────────────────────────────
 
   speedSlider.addEventListener('input', function () {
     speedLabel.textContent = parseFloat(speedSlider.value).toFixed(1) + '\u00D7';
+    localStorage.setItem(LS_SPEED, speedSlider.value);
+  });
+
+  voiceSel.addEventListener('change', function () {
+    localStorage.setItem(LS_VOICE, voiceSel.value);
+  });
+
+  autoplayChk.addEventListener('change', function () {
+    localStorage.setItem(LS_AUTONEXT, autoplayChk.checked ? 'true' : 'false');
   });
 
   // ── paragraph indexing ───────────────────────────────────────────────────────