feat(notifications): web push + telegram/discord stream alerts

[bright5455]

closes #1474

• backend: NotificationService fans out to Web Push, Telegram and Discord
• backend: NotificationBotWorker polls active streams for <24h runway
• backend: /api/v1/notifications endpoints via Express router
• backend: Prisma models (PushSubscription, NotificationChannel, LinkCode, NotificationLog)
• frontend: sw.js service worker handling push + notificationclick
• frontend: push.ts VAPID helper
• frontend: PushNotificationToggle + /settings/notifications page
• tests: urlBase64ToUint8Array decoding + toggle lifecycle

Description

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔧 Refactoring (no functional changes)
• ⚡ Performance improvement
• 🧪 Test addition or update

Related Issues

Closes #

Changes Made

Testing

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Test Steps

Breaking Changes

Breaking Changes:

Migration Guide:

Screenshots/Demo

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Updated Postman/Hoppscotch API collections if routes changed
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published
• I have checked for breaking changes and documented them if applicable
• If this change adds or modifies a metric, I have updated the Grafana dashboard and the alert rules in backend/docs/observability/

Additional Notes