* feat: add customizable reminder email templates
- Add SubmitterMailer#reminder_email with separate subject/body resolution
- Support per-template and per-account reminder email customization
- Add GUI forms for reminder email templates (account + template level)
- Add i18n keys for reminder emails and reminder visibility UI
- Update SendSubmitterReminderEmailJob to use reminder_email instead of invitation_email
- Add race condition guard (1-minute dedup) in send job
* fix: prevent reminder job duplication on container restart
- Add deduplication in scheduled_jobs.rb initializer (clear existing before scheduling)
- Add reschedule! method in ProcessSubmitterRemindersJob that clears stale copies
- Prevents exponential job accumulation across container restarts
* feat: add reminder visibility and queue management
- Add SubmitterReminders module (lib/) for next-reminder-at calculation
- Show next reminder time per submitter on submission page (with timezone tooltip)
- Add pending reminders queue table on notifications settings page
- Add Skip button to advance past current pending reminder (Turbo Stream)
- Add skip_reminder_email event type to SubmissionEvent
- Update ProcessSubmitterRemindersJob to count skip events in reminder_count
- Add SubmitterRemindersController with destroy action for skip
* docs: document reminder email templates feature in README
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Co-authored-by: Sebastian Noe <sebastian.schneider@boxine.de>