Add configurable notifications via email

[dividing-by-zaro]

Overview

Add an email notification system that alerts users when significant changes occur in their tracked repositories. Notifications should be real-time for major/breaking changes and digest-style for minor updates.

Goals

• Keep users informed about important repo changes without requiring them to check the feed
• Provide flexibility in how and when users receive notifications
• Support email as a notification channel

Features

Notification Triggers

• Immediate notifications for:
  • Major/breaking changes (significance: major)
  • Security updates
  • New releases
• Digest notifications (daily/weekly configurable) for:
  • Minor and patch updates
  • Feature additions and enhancements
  • Bug fixes

Email Notifications

• Beautiful HTML email templates matching the app's neo-brutalist design
• Configurable frequency: immediate (for major), daily digest, weekly digest, or off
• Unsubscribe link in every email
• Email verification before enabling

User Settings

• Global notification preferences (default for all repos)
• Per-repo overrides (e.g., turn off notifications for a specific repo)
• Quiet hours / timezone awareness

Technical Considerations

• Queue-based notification processing (avoid blocking the main app)
• Rate limiting for email provider calls
• Batch digest emails efficiently
• Store notification preferences in User and UserRepo tables
• Track notification history for debugging/user reference

Out of Scope (for now)

• Mobile push notifications
• In-app notification center
• Slack notifications (see separate issue)