EPUB reader: font picker + performance fixes for large books

- Add font family selector (Serif/Sans/Verdana/Mono) to reader settings panel,
  saved per book in localStorage
- Strip <style>/<script> blocks before regex and DOMParser processing to avoid
  working over large base64-embedded font CSS in publisher EPUBs
- Parallelize image blob URL creation with Promise.all instead of sequential await
- Inject chapter HTML progressively in batches with requestAnimationFrame yields
  to keep the UI responsive when loading many-chapter books

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

static/js/app.js

@@ -2467,38 +2467,45 @@ async function parseEpub(arrayBuffer) {
     };
   });
 
-  // 4. Build image map: abs zip path → blob URL
+  // 4. Build image map: abs zip path → blob URL (parallel)
   const imageMap = {};
-  for (const {href, mediaType} of Object.values(manifest)) {
-    if (mediaType.startsWith('image/')) {
-      try {
-        const buf = await zip.file(href).async('arraybuffer');
-        imageMap[href] = URL.createObjectURL(new Blob([buf], {type: mediaType}));
-      } catch (e) { /* missing asset */ }
-    }
-  }
+  await Promise.all(
+    Object.values(manifest)
+      .filter(({mediaType}) => mediaType.startsWith('image/'))
+      .map(async ({href, mediaType}) => {
+        try {
+          const buf = await zip.file(href).async('arraybuffer');
+          imageMap[href] = URL.createObjectURL(new Blob([buf], {type: mediaType}));
+        } catch (e) { /* missing asset */ }
+      })
+  );
 
   // 5. Parse TOC
   const toc = await _parseEpubToc(zip, opfDoc, manifest);
 
-  // 6. Get spine and concatenate chapters
+  // 6. Get spine items; chapters are returned raw for progressive DOM injection
   const spineItems = Array.from(opfDoc.querySelectorAll('spine > itemref'))
     .map(ref => manifest[ref.getAttribute('idref')]?.href)
     .filter(Boolean);
 
-  const parts = [];
+  const chapters = [];
   for (let i = 0; i < spineItems.length; i++) {
     const href = spineItems[i];
     try {
-      const chapterText = await zip.file(href).async('text');
+      let chapterText = await zip.file(href).async('text');
+      // Strip style/script blocks early — publisher EPUBs often embed large base64 fonts in CSS.
+      // This shrinks the string before regex and DOMParser work on it.
+      chapterText = chapterText.replace(/<style\b[^>]*>[\s\S]*?<\/style>/gi, '');
+      chapterText = chapterText.replace(/<script\b[^>]*>[\s\S]*?<\/script>/gi, '');
       const chapterDir = href.includes('/') ? href.substring(0, href.lastIndexOf('/') + 1) : '';
       const withBlobs = _injectImageBlobs(chapterText, chapterDir, imageMap);
       const sanitized = sanitizeEpubHtml(withBlobs);
-      parts.push(`<div id="epub-chapter-${i}" data-epub-src="${href}">${sanitized}</div>`);
+      chapters.push(`<div id="epub-chapter-${i}" data-epub-src="${href}">${sanitized}</div>`);
+      if (i % 8 === 0) await new Promise(r => requestAnimationFrame(r));
     } catch (e) { /* skip missing */ }
   }
 
-  return {title, author, html: parts.join('\n'), toc, imageMap};
+  return {title, author, chapters, toc, imageMap};
 }
 
 async function _parseEpubToc(zip, opfDoc, manifest) {
@@ -2736,6 +2743,7 @@ async function _evictBookCache(bookList) {
 
 // Reader settings
 let readerSettings = { fontSize: 16, lineHeight: 1.8, maxWidth: 65, theme: 'dark',
+                        fontFamily: 'serif',
                         pdfZoom: 100, pdfInverted: false, pdfPaginated: false, pdfSpread: false };
 let readerSettingsPanelOpen = false;
 let currentPdfDoc = null;
@@ -3196,7 +3204,18 @@ async function openBook(bookId) {
       author = result.author || author;
       toc = result.toc;
       currentImageMap = result.imageMap;
-      contentEl.innerHTML = result.html;
+      // Inject chapters progressively so the browser stays responsive on large books
+      const BATCH = 8;
+      for (let i = 0; i < result.chapters.length; i += BATCH) {
+        const frag = document.createDocumentFragment();
+        const tmp = document.createElement('div');
+        for (let j = i; j < Math.min(i + BATCH, result.chapters.length); j++) {
+          tmp.innerHTML = result.chapters[j];
+          while (tmp.firstChild) frag.appendChild(tmp.firstChild);
+        }
+        contentEl.appendChild(frag);
+        await new Promise(r => requestAnimationFrame(r));
+      }
     }
 
     currentBookToc = toc;
@@ -3561,6 +3580,7 @@ function jumpToTocEntry(href) {
 function loadReaderSettings(bookId) {
   // Reset to defaults, then apply per-book overrides
   Object.assign(readerSettings, { fontSize: 16, lineHeight: 1.8, maxWidth: 65, theme: 'dark',
+                                   fontFamily: 'serif',
                                    pdfZoom: 100, pdfInverted: false, pdfPaginated: false, pdfSpread: false });
   try {
     const saved = JSON.parse(localStorage.getItem(`diora_reader_settings_${bookId}`) || '{}');
@@ -3586,6 +3606,13 @@ function applyReaderSettings(isPdf) {
     contentEl.style.fontSize = readerSettings.fontSize + 'px';
     contentEl.style.lineHeight = readerSettings.lineHeight;
     contentEl.style.setProperty('--reader-max-width', readerSettings.maxWidth + 'ch');
+    const fontMap = {
+      serif:    "Georgia, 'Times New Roman', serif",
+      sans:     'system-ui, -apple-system, sans-serif',
+      humanist: 'Verdana, Geneva, sans-serif',
+      mono:     "'Courier New', monospace",
+    };
+    contentEl.style.fontFamily = fontMap[readerSettings.fontFamily] || fontMap.serif;
     if (_currentPositionAnchor && currentBookId) {
       requestAnimationFrame(() => restoreFromAnchor($('reader-content'), _currentPositionAnchor));
     }
@@ -3626,6 +3653,10 @@ function toggleSettingsPanel() {
       <label>Line <input type="range" id="rs-line" min="12" max="30" step="1" value="${Math.round(readerSettings.lineHeight * 10)}"> <span id="rs-line-val">${readerSettings.lineHeight}</span></label>
       <label>Width <input type="range" id="rs-width" min="40" max="90" step="5" value="${readerSettings.maxWidth}"> <span id="rs-width-val">${readerSettings.maxWidth}ch</span></label>
       <button class="btn btn-sm" id="rs-width-full">Full</button>
+      <button class="btn btn-sm ${readerSettings.fontFamily === 'serif'    ? 'active' : ''}" data-rs-font="serif">Serif</button>
+      <button class="btn btn-sm ${readerSettings.fontFamily === 'sans'     ? 'active' : ''}" data-rs-font="sans">Sans</button>
+      <button class="btn btn-sm ${readerSettings.fontFamily === 'humanist' ? 'active' : ''}" data-rs-font="humanist">Verdana</button>
+      <button class="btn btn-sm ${readerSettings.fontFamily === 'mono'     ? 'active' : ''}" data-rs-font="mono">Mono</button>
       <button class="btn btn-sm ${readerSettings.theme === 'dark'   ? 'active' : ''}" data-rs-theme="dark">Dark</button>
       <button class="btn btn-sm ${readerSettings.theme === 'sepia'  ? 'active' : ''}" data-rs-theme="sepia">Sepia</button>
       <button class="btn btn-sm ${readerSettings.theme === 'bright' ? 'active' : ''}" data-rs-theme="bright">Bright</button>
@@ -3676,6 +3707,15 @@ function toggleSettingsPanel() {
       saveReaderSettings();
     });
 
+    panel.querySelectorAll('[data-rs-font]').forEach(btn => {
+      btn.addEventListener('click', () => {
+        readerSettings.fontFamily = btn.dataset.rsFont;
+        panel.querySelectorAll('[data-rs-font]').forEach(b => b.classList.toggle('active', b === btn));
+        applyReaderSettings(false);
+        saveReaderSettings();
+      });
+    });
+
     panel.querySelectorAll('[data-rs-theme]').forEach(btn => {
       btn.addEventListener('click', () => {
         readerSettings.theme = btn.dataset.rsTheme;