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.test.js

@@ -0,0 +1,44 @@
+import { afterEach, beforeEach, expect, test, vi } from 'vitest';
+import { bibleRefs, bookRefs, canSaveOffline, downloadChapters, loadSavedBooks, markBookSaved } from './offline.js';
+
+beforeEach(() => localStorage.clear());
+afterEach(() => vi.unstubAllGlobals());
+
+const chapterResponse = { ok: true, json: () => Promise.resolve({ chapter: { content: [{ type: 'verse', number: 1, content: ['In the beginning.'] }] } }) };
+
+test('lists every chapter of a book and of the whole Bible', () => {
+  expect(bookRefs('JHN')).toHaveLength(21);
+  expect(bookRefs('JHN')[0]).toEqual({ book: 'JHN', chapter: 1 });
+  expect(bibleRefs()).toHaveLength(1189);
+});
+
+test('only the free translations can be saved', () => {
+  expect(canSaveOffline('BSB')).toBe(true);
+  expect(canSaveOffline('NET')).toBe(true);
+  expect(canSaveOffline('ESV')).toBe(false);
+});
+
+test('remembers which books are saved', () => {
+  markBookSaved('BSB', 'JHN');
+  markBookSaved('BSB', 'JHN');
+  markBookSaved('BSB', 'PSA');
+  expect(loadSavedBooks()).toEqual({ BSB: ['JHN', 'PSA'] });
+});
+
+test('downloads every chapter, reports progress, and keeps going past a failure', async () => {
+  const fetchMock = vi.fn((url) => Promise.resolve(url.includes('/JHN/2.json') ? { ok: false } : chapterResponse));
+  vi.stubGlobal('fetch', fetchMock);
+  const progress = [];
+  const result = await downloadChapters('BSB', bookRefs('JHN').slice(0, 4), { onProgress: (d, t) => progress.push([d, t]) });
+  expect(result).toEqual({ done: 3, failed: 1 });
+  expect(fetchMock).toHaveBeenCalledTimes(4);
+  expect(progress.at(-1)).toEqual([4, 4]);
+});
+
+test('stops when told to', async () => {
+  const controller = new AbortController();
+  const fetchMock = vi.fn(() => { controller.abort(); return Promise.resolve(chapterResponse); });
+  vi.stubGlobal('fetch', fetchMock);
+  await downloadChapters('BSB', bookRefs('PSA'), { signal: controller.signal, concurrency: 1 });
+  expect(fetchMock.mock.calls.length).toBeLessThan(5);
+});