1. Infrastructure

• [x] 1.1 Add outbox and notification_preferences tables (migration 0038)
• [x] 1.2 Add SMTP settings to config and deployment secrets

2. Notifier

• [x] 2.1 Emit assignment events to the outbox inside the assignment transaction
• [x] 2.2 Implement cmd/notifier worker that drains the outbox and sends email
• [x] 2.3 Skip self-assignments and opted-out recipients

3. Preferences UI

• [x] 3.1 Add per-project "Email me about assignments" toggle to project settings
• [x] 3.2 Add integration test covering opt-out