Tiered Timer.periodic instances (1min, 10min, 15min, 1hr, midnight)
running on a dedicated Dart isolate. Tick messages sent back to the
main isolate via SendPort and emitted as SchedulerTick events on the
DaemonBus. Extensions subscribe with events.on<SchedulerTick>() and
filter by tier.
Co-Authored-By: Claude <noreply@anthropic.com>
