Users can now mute specific notification categories (assignments, status
changes, comments & mentions, priority/due-date updates, agent activity)
from Settings > Notifications. Muted event types are silently filtered at
notification creation time — no inbox items are created for muted groups.
- Add notification_preference table (migration 064)
- Add GET/PUT /api/notification-preferences endpoints
- Filter notifications in notifyIssueSubscribers, notifyDirect, and
notifyMentionedMembers based on user preferences
- Add Notifications tab in Settings with per-group toggle switches
