Add email as a second notification channel alongside ntfy:
- Tabbed channel selector: ntfy | Email | Telegram (coming soon) | Discord (coming soon)
- Active channel shown with green status dot on tab
- Email tab: address input, Save & Enable, Test, Disable — same UX pattern as ntfy
- Backend: SMTP config in settings (SMTP_HOST/PORT/USER/PASSWORD/FROM/STARTTLS)
- Dispatcher: _send_email() helper wired into dispatch_notifications
- POST /api/notifications/test/email endpoint with descriptive error messages
- Email fires in same window as ntfy (respects quiet hours / digest hold)
- Telegram and Discord tabs show coming-soon banners with planned feature description
- .env.example documents all SMTP settings with provider examples
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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