Add Outline stage, parallel reading, offline saves, backup, sync-conflict handling and more

Study
- New Outline stage (hierarchical I./A./1. points, linked to chunks, in all exports);
  the chunk stage is now "Chunks"
- Home cards: passages shown as ranges, tags capped with "+N more"

Reader
- Side-by-side translations and a Compare tab per verse
- Typeface, line spacing, verse-number settings; text and column scale with the screen
- Highlights/bookmarks sheet with named colours (synced); BSB footnote spacing fix
- Cmd-K palette (passages, studies, notes, marks), keyboard shortcuts and "?" help

Flow and safety
- Toasts with Undo replace most confirm()/alert()
- Back/Forward move between pages
- Server refuses saves over a newer copy (409); keep-mine / use-other banner;
  opening a study no longer re-stamps it
- Latest chapter request wins when flipping quickly

Offline and data
- Save books, plan days or a whole BSB/NET for offline
- Service worker fixes: helloao /api/ URLs were skipped and responses cloned too late
- Settings: download/restore a full backup

Accessibility
- Sheets trap focus and close on Escape, skip link, focus ring, reduced motion,
  theme contrast raised to 4.5:1 (with a test)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/utils/offline.js

@@ -0,0 +1,45 @@
+// "Save for offline": fetch chapters ahead of time so they open without a connection. Fetching is
+// all it takes — the service worker (public/sw.js) keeps every Bible-text response it sees. Only the
+// free translations (BSB, NET) can be saved; the licensed ones' terms don't allow bulk copies.
+import { CHAPTER_COUNTS } from './bibleUtils.jsx';
+import { fetchChapter, isLicensed } from './bibleText.js';
+
+const KEY = 'offline-saved';
+
+// { 'BSB': ['JHN', 'PSA'] }: whole books saved on this device, per translation.
+export function loadSavedBooks() {
+  try {
+    const raw = JSON.parse(localStorage.getItem(KEY) || '{}');
+    return raw && typeof raw === 'object' && !Array.isArray(raw) ? raw : {};
+  } catch { return {}; }
+}
+
+export function markBookSaved(translation, book) {
+  const all = loadSavedBooks();
+  all[translation] = [...new Set([...(all[translation] ?? []), book])];
+  try { localStorage.setItem(KEY, JSON.stringify(all)); } catch { /* storage full or unavailable */ }
+  return all;
+}
+
+export const canSaveOffline = (translation) => !isLicensed(translation);
+
+export const bookRefs = (book) => Array.from({ length: CHAPTER_COUNTS[book] ?? 0 }, (_, i) => ({ book, chapter: i + 1 }));
+export const bibleRefs = () => Object.keys(CHAPTER_COUNTS).flatMap(bookRefs);
+
+// Fetches every chapter in `refs` ([{ book, chapter }]) a few at a time, calling onProgress(done, total)
+// as each lands. Resolves { done, failed } — a chapter that fails doesn't stop the rest. Pass `signal`
+// to stop early.
+export async function downloadChapters(translation, refs, { onProgress, signal, concurrency = 4 } = {}) {
+  const queue = [...refs];
+  let done = 0;
+  let failed = 0;
+  const worker = async () => {
+    while (queue.length > 0 && !signal?.aborted) {
+      const { book, chapter } = queue.shift();
+      try { await fetchChapter(translation, book, chapter, { signal }); done += 1; } catch { if (!signal?.aborted) failed += 1; }
+      onProgress?.(done + failed, refs.length);
+    }
+  };
+  await Promise.all(Array.from({ length: Math.min(concurrency, refs.length) }, worker));
+  return { done, failed };
+}