clearHomeCache method
Clears all home first-paint cache entries. Called on sign-out so the next user doesn't see the previous user's streak / domain list flash before their own data loads.
Implementation
Future<void> clearHomeCache() async {
final p = await _prefs();
await Future.wait([
p.remove(_homeStreakKey),
p.remove(_homeDueCountKey),
p.remove(_homeDomainsKey),
]);
}