feat: Seaca mobile API, enrollment, FCM push and admin UI (0.9.0)

Adds mobile device registration by admin codes, refresh tokens, push channel
in notification policy, and Settings section for managing Seaca clients.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/test_problems.py

@@ -4,6 +4,7 @@ import uuid
 from datetime import datetime, timedelta, timezone
 
 from app.models import Host, Problem
+from tests.test_ingest import VALID_EVENT
 
 
 def _event_payload(**overrides):