feat(settings): sync preferences across devices via io.lotus.settings account data (#104)

Every Lotus setting was localStorage-only, so a user on web + desktop + phone
configured theme, composer toolbar, quiet hours, call keys… three times.

- utils/settingsSync.ts (pure, 7 tests): DEVICE_LOCAL_KEYS denylist (zoom,
  media auto-load, animation pause, glassmorphism, denoise tier/model,
  bitrates, volumes, notification permission, developer tools, PTT mode,
  camera-on-join, drawer state, and the sync toggle itself), pickSyncable,
  mergeRemoteSettings (unknown keys, device-local keys and wrong-shaped
  values are skipped), buildSyncedContent, shouldApplyRemote (LWW on
  updatedAt; equal stamp = our own echo).
- hooks/useSettingsSync.ts: on start applies a newer remote snapshot or
  pushes local if it differs; debounced push on any settingsAtom write,
  skipped when the syncable subset equals the last pushed/applied snapshot
  so a remote apply never echoes back; AccountData listener for live
  updates; stamps forced monotonic per device; per-account lastSyncedAt
  marker so another user on the same device can't inherit it; failed pushes
  roll the marker back so the next change retries. Remote values are re-read
  through getSettings() so enum coercion applies.
- Settings → General → Sync: toggle (device-local), "Push now", "Clear
  synced copy". AccountDataEvent.LotusSettings registered.
- ClientNonUIFeatures: the #103 tracking-param subscriber moves out of
  PageZoomFeature into its own TrackingParamsFeature next to
  SettingsSyncFeature.
- Docs: LOTUS_FEATURES entries for #103/#104; LOTUS_TODO links the new
  Features 2026-Q4 milestone and #108.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/types/matrix/accountData.ts

@@ -23,6 +23,9 @@ export enum AccountDataEvent {
   // global default behavior for threads.
   LotusThreadNotifications = 'io.lotus.thread_notifications',
 
+  // [Gitea #104] Synced subset of the Lotus Settings object (utils/settingsSync).
+  LotusSettings = 'io.lotus.settings',
+
   SecretStorageDefaultKey = 'm.secret_storage.default_key',
 
   CrossSigningMaster = 'm.cross_signing.master',