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/components/ShortcutsHelp.jsx

@@ -0,0 +1,63 @@
+// The "?" cheat sheet: every keyboard shortcut for the page you are on, plus the ones that work everywhere.
+import { useEffect, useRef } from 'react';
+import { useApp } from '../context/AppContext.js';
+import { themeVars } from './reader/readerThemes.js';
+
+const GLOBAL = [
+  ['⌘K  /  Ctrl K', 'Search and go to a passage'],
+  ['?', 'Show this list'],
+  ['Esc', 'Close whatever is open'],
+];
+const BY_PAGE = {
+  reader: [
+    ['← →', 'Previous / next chapter'],
+    ['/', 'Search this chapter or the whole Bible'],
+    ['G', 'Pick a book and chapter'],
+    ['B', 'Bookmark the selected verse'],
+    [',', 'Reading settings'],
+    ['F', 'Hide or show the controls'],
+  ],
+  study: [
+    ['← →', 'Previous / next chunk'],
+  ],
+};
+
+export default function ShortcutsHelp({ onClose }) {
+  const { readerTheme, currentPage } = useApp();
+  const closeRef = useRef(null);
+  useEffect(() => {
+    const from = document.activeElement;
+    closeRef.current?.focus();
+    const onKey = (e) => { if (e.key === 'Escape' || e.key === '?') { e.preventDefault(); e.stopPropagation(); onClose(); } };
+    document.addEventListener('keydown', onKey, true);
+    return () => { document.removeEventListener('keydown', onKey, true); if (from instanceof HTMLElement && document.contains(from)) from.focus({ preventScroll: true }); };
+  }, [onClose]);
+
+  const page = BY_PAGE[currentPage] ?? [];
+  const section = (title, rows) => (
+    <div className="mb-4 last:mb-0">
+      <h3 className="mb-1.5 text-[11px] uppercase tracking-wide text-[var(--r-sub)]">{title}</h3>
+      <dl className="space-y-1.5">
+        {rows.map(([keys, what]) => (
+          <div key={keys} className="flex items-center justify-between gap-4 text-sm">
+            <dt><kbd className="rounded-md border border-[var(--r-line)] bg-[var(--r-bg)] px-2 py-0.5 font-mono text-xs">{keys}</kbd></dt>
+            <dd className="text-right text-[var(--r-sub)]">{what}</dd>
+          </div>
+        ))}
+      </dl>
+    </div>
+  );
+
+  return (
+    <div style={themeVars(readerTheme)} className="fixed inset-0 z-[90] flex items-center justify-center bg-black/40 px-3 font-sans" onMouseDown={(e) => { if (e.target === e.currentTarget) onClose(); }}>
+      <div role="dialog" aria-modal="true" aria-label="Keyboard shortcuts" className="max-h-[80vh] w-full max-w-sm overflow-y-auto rounded-2xl border border-[var(--r-line)] bg-[var(--r-bar)] p-5 text-[var(--r-text)] shadow-2xl">
+        <div className="mb-3 flex items-center justify-between">
+          <h2 className="text-base font-medium">Keyboard shortcuts</h2>
+          <button ref={closeRef} type="button" onClick={onClose} className="rounded-lg px-2 py-1 text-sm text-[var(--r-sub)] hover:bg-black/5">Close</button>
+        </div>
+        {page.length > 0 && section(currentPage === 'reader' ? 'In the Bible' : 'In this study', page)}
+        {section('Everywhere', GLOBAL)}
+      </div>
+    </div>
+  );
+}