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_notification_policy.py

@@ -25,6 +25,7 @@ def test_put_policy_persists_db(jwt_headers, client, db_session, monkeypatch):
             "use_telegram": True,
             "use_webhook": True,
             "use_email": False,
+            "use_mobile": False,
         },
     )
     assert response.status_code == 200
@@ -58,6 +59,7 @@ def test_upsert_policy_syncs_channel_min_severity(db_session, monkeypatch):
         use_telegram=True,
         use_webhook=False,
         use_email=False,
+        use_mobile=False,
     )
     row = db_session.get(NotificationChannel, "telegram")
     assert row.min_severity == "critical"