Add docs/plugin-feedback-android-duplicate-reminder-notification.md
describing the duplicate notification on first-time reminder setup (one
correct + one fallback). Root cause: ScheduleHelper schedules the
static reminder alarm and also enqueues the prefetch worker, which
on fallback schedules a second alarm via DailyNotificationScheduler.
Suggested fix: for static-reminder schedules, do not enqueue prefetch
(or have prefetch skip scheduleNotificationIfNeeded). The suggested
plugin changes were applied and fixed the issue.
