Migrate StateNotifierProvider/StateNotifier → NotifierProvider/Notifier,
StateProvider → NotifierProvider with simple notifier, FamilyAsyncNotifier
removed in Riverpod 3 (replaced with constructor-arg pattern), and rename
.valueOrNull → .value throughout all providers and screens.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>