PR2: Background Workers implementation
- Update DailyNotificationFetchWorker to use NativeNotificationContentFetcher SPI
- Remove TimeSafari coordination checks from worker (moved to host app)
- Add fetchContentWithTimeout() method that calls native fetcher via SPI
- Add fallback to legacy fetcher if no native fetcher is registered
- Update handleSuccessfulFetch() to process List<NotificationContent>
- Simplify retry logic to use SchedulingPolicy for exponential backoff
- Remove all TimeSafari-specific coordination methods from worker
- Add static getter in DailyNotificationPlugin for worker access to native fetcher
This completes the worker-side implementation of the dual-path SPI,
allowing background workers to reliably fetch content using native code.
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