feat(automation): saved searches with email/in-app notifications

[paruff]

Problem

Pros need to be notified instantly when a property matching their criteria hits the market. Manual polling is too slow for competitive markets.

Acceptance Criteria

• Create SavedSearch model: user, name, criteria (JSON), notification_frequency (immediate/daily/weekly), is_active
• Create core/services/search_alerts.py with run_saved_searches() and send_notification(user, property, search)
• Add management command: python manage.py run_saved_searches --frequency=immediate
• Email notification via Django's email backend (SMTP configurable)
• In-app notification center at /notifications/ with unread badge
• Allow user to configure frequency per search (immediate / daily digest / weekly digest)
• Deduplicate: don't notify twice for same property
• E2E test: create saved search, trigger discovery, verify notification appears
• Unit tests for search matching and deduplication logic

Implementation Guide (for opencode/mimo v2.5)

1. Create SavedSearch model in core/models/discovery.py
2. Create core/services/search_alerts.py with matching + notification logic
3. Create core/management/commands/run_saved_searches.py
4. Add notification center view at /notifications/
5. Add notifications/ URL and template
6. Add Celery/Redis task for immediate notifications (or cron for daily/weekly)

Dependencies

• Requires: Discovery pipeline data sources (MLS, Rentometer, ATTOM)
• Requires: Email backend configured (SMTP)
• Enhances: Phase 1 data feeds (makes them actionable)