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/hooks/useReadingPlans.js

@@ -6,6 +6,8 @@
 // shown, instead of being a fire-and-forget call buried inside setState.
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 import { getRemoteReadingProgress, saveRemoteReadingProgress } from '../syncService.js';
+import { useToast } from '../components/Toasts.jsx';
+import { mergeReadingPlans } from '../utils/backup.js';
 import { clampPlanDays, localDateString, normalizeCustomPlan, registerCustomPlans } from '../utils/readingPlans.js';
 
 const STORAGE_KEY = 'readingPlanProgress';
@@ -33,7 +35,10 @@ function formatSyncError(result) {
 }
 
 export function useReadingPlans() {
+  const { toast } = useToast();
   const [state, setState] = useState(loadLocal);
+  const stateRef = useRef(state); // the latest state, for taking a copy just before something is removed
+  stateRef.current = state;
   const [syncStatus, setSyncStatus] = useState(''); // '' | 'syncing' | 'synced' | 'error'
   const [syncError, setSyncError] = useState('');
   // The exact object loadLocal() produced at mount. Compared by reference (not
@@ -167,17 +172,30 @@ export function useReadingPlans() {
     updateProgress((prev) => prev.map((p) => (p.id === progressId ? { ...p, translation } : p)));
   }, [updateProgress]);
 
+  // Restarting and removing are immediate, with an "Undo" toast that puts the plan back exactly as it was.
   const restartPlan = useCallback((progressId) => {
+    const before = stateRef.current.progress.find((p) => p.id === progressId);
     updateProgress((prev) => prev.map((p) => (
       p.id === progressId
         ? { ...p, completedDays: [], chaptersRead: {}, completedAt: null, startedAt: Date.now(), lastActivityAt: Date.now() }
         : p
     )));
-  }, [updateProgress]);
+    if (before) toast('Plan restarted from day 1', { action: { label: 'Undo', onClick: () => updateProgress((prev) => prev.map((p) => (p.id === progressId ? before : p))) } });
+  }, [updateProgress, toast]);
 
   const removePlanProgress = useCallback((progressId) => {
+    const index = stateRef.current.progress.findIndex((p) => p.id === progressId);
+    const before = stateRef.current.progress[index];
     updateProgress((prev) => prev.filter((p) => p.id !== progressId));
-  }, [updateProgress]);
+    if (before) {
+      toast('Plan removed', {
+        action: {
+          label: 'Undo',
+          onClick: () => updateProgress((prev) => (prev.some((p) => p.id === progressId) ? prev : [...prev.slice(0, index), before, ...prev.slice(index)])),
+        },
+      });
+    }
+  }, [updateProgress, toast]);
 
   // Resets the pace clock so a plan that's fallen behind schedule stops being
   // flagged as "behind" — doesn't touch which days are actually marked done.
@@ -212,9 +230,22 @@ export function useReadingPlans() {
   }, [updateCustomPlans]);
 
   const removeCustomPlan = useCallback((planId) => {
+    const plan = stateRef.current.customPlans.find((p) => p.id === planId);
+    const runs = stateRef.current.progress.filter((p) => p.planId === planId);
     updateCustomPlans((prev) => prev.filter((p) => p.id !== planId));
     updateProgress((prev) => prev.filter((p) => p.planId !== planId));
-  }, [updateCustomPlans, updateProgress]);
+    if (plan) {
+      toast(`Deleted “${plan.title}”`, {
+        action: {
+          label: 'Undo',
+          onClick: () => {
+            updateCustomPlans((prev) => (prev.some((p) => p.id === planId) ? prev : [plan, ...prev]));
+            updateProgress((prev) => [...runs.filter((r) => !prev.some((p) => p.id === r.id)), ...prev]);
+          },
+        },
+      });
+    }
+  }, [updateCustomPlans, updateProgress, toast]);
 
   // Patches an existing custom plan. Pass resetProgress: true when the edit
   // changes its books/days (day indices from before the edit no longer mean
@@ -230,6 +261,11 @@ export function useReadingPlans() {
     }
   }, [updateCustomPlans, updateProgress]);
 
+  // Plans from a backup file are added to what is here (nothing is removed).
+  const importReadingPlans = useCallback((incoming) => {
+    setState((prev) => ({ ...prev, ...mergeReadingPlans(prev, incoming) }));
+  }, []);
+
   // Server wins over whatever's local at sign-in.
   const mergeServerReadingProgress = useCallback((serverData) => {
     if (!serverData || typeof serverData !== 'object' || Array.isArray(serverData)) {
@@ -280,6 +316,8 @@ export function useReadingPlans() {
   }, [state]);
 
   return {
+    readingPlansState: state,
+    importReadingPlans,
     planProgress: state.progress,
     customPlans,
     readingActivity: state.activity,