Sync bookmarks, highlights and display preferences to the account

Bookmarks and text highlights are saved per user and merged across devices
(union on first contact, newer server copy when this device is clean). Theme,
default translation, verse layout, commentary source and reading position sync
too, each with its own timestamp so the newest change to each setting wins.
The Reader never moves under you while it is open. Signing out clears this
device's marks and forgets sync timestamps.

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

server/db.js

@@ -97,6 +97,25 @@ export function initDb() {
     );
   `);
 
+  // Display preferences (theme, default translation, layout, ...) — one row per user.
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS user_prefs (
+      user_id    TEXT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+      data       TEXT NOT NULL,
+      updated_at INTEGER NOT NULL
+    );
+  `);
+
+  // Reader bookmarks + text highlights — one row per user (small JSON), so they follow the
+  // user across devices. updated_at lets a device tell whether the server copy is newer.
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS reader_marks (
+      user_id    TEXT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+      data       TEXT NOT NULL,
+      updated_at INTEGER NOT NULL
+    );
+  `);
+
   // Reading plan progress — one row per user, holding the whole list of
   // in-progress/completed plans as JSON (small; no need to normalize).
   db.exec(`
@@ -228,6 +247,39 @@ export function getAllReaderInk(userId) {
   );
 }
 
+/** The user's synced preferences: { key: { v, at } } (empty when none saved yet). */
+export function getUserPrefs(userId) {
+  const row = db.prepare('SELECT data FROM user_prefs WHERE user_id = ?').get(userId);
+  return row ? JSON.parse(row.data) : {};
+}
+
+/** Replaces the user's stored preferences with `prefs` ({ key: { v, at } }). */
+export function setUserPrefs(userId, prefs) {
+  db.prepare(`
+    INSERT INTO user_prefs (user_id, data, updated_at) VALUES (?, ?, ?)
+    ON CONFLICT(user_id) DO UPDATE SET data = excluded.data, updated_at = excluded.updated_at
+  `).run(userId, JSON.stringify(prefs), Date.now());
+}
+
+/** The user's bookmarks + highlights: { bookmarks, highlights, updatedAt } (updatedAt 0 = never saved). */
+export function getReaderMarks(userId) {
+  const row = db.prepare('SELECT data, updated_at AS updatedAt FROM reader_marks WHERE user_id = ?').get(userId);
+  if (!row) return { bookmarks: {}, highlights: [], updatedAt: 0 };
+  const data = JSON.parse(row.data);
+  return { bookmarks: data.bookmarks ?? {}, highlights: data.highlights ?? [], updatedAt: row.updatedAt };
+}
+
+/** Replaces the user's bookmarks + highlights; returns the new updatedAt (always moves forward). */
+export function setReaderMarks(userId, { bookmarks, highlights }) {
+  const prev = db.prepare('SELECT updated_at AS updatedAt FROM reader_marks WHERE user_id = ?').get(userId);
+  const updatedAt = Math.max(Date.now(), (prev?.updatedAt ?? 0) + 1);
+  db.prepare(`
+    INSERT INTO reader_marks (user_id, data, updated_at) VALUES (?, ?, ?)
+    ON CONFLICT(user_id) DO UPDATE SET data = excluded.data, updated_at = excluded.updated_at
+  `).run(userId, JSON.stringify({ bookmarks, highlights }), updatedAt);
+  return updatedAt;
+}
+
 /** Upserts the ink strokes for one reader page. */
 export function setReaderInkPage(userId, bookAbbrev, chapter, strokes) {
   db.prepare(`