Theme, reduce-motion and board labels lived only in local IndexedDB/localStorage,
so they did not follow the user across devices and could be lost when the Telegram
WebView cleared storage.
Mirror these three device-independent prefs to Telegram CloudStorage (Bot API 6.9)
from the single local-persist point (persistPrefs), and reconcile them from
CloudStorage in the background on launch (reconcileCloudPrefs) so a change made on
another device follows the user here. The local store stays the instant-render
cache; the interface language is intentionally excluded (it syncs via the durable
account). Pure encode/decode extracted to cloudprefs.ts with unit tests; the
CloudStorage transport wrappers are added to telegram.ts. No-op outside Telegram or
on a client predating CloudStorage.
Ilia Denisov