Prevents a second notification (UUID alarm) with fallback or placeholder text by
cancelling pending prefetch/fetch work when the user schedules or reschedules.
cleanupExistingNotificationSchedules only cancels alarms for DB schedule IDs;
alarms from DailyNotificationFetchWorker use a UUID and were never cancelled.
Add ScheduleHelper.cancelFetchRelatedWorkManagerJobs() to cancel only the
prefetch and daily_notification_fetch tags (not display, dismiss, or maintenance).
Call it after cleanup and before scheduleDailyNotification. Future fetched-content
flows can use distinct WorkManager tags and will not be affected by this path.
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