Get Fraud Alerts

Get recent fraud alerts for admin monitoring. Sync (def) so cold-cache fills run in the threadpool, not on the event loop.

Deliberately NOT segmented. Every fraud_alerts row on gamma carries a NULL user_id (517 of 517, checked 2026-09-02) — the alerts are raised against signals, not attributed to an account. Filtering them by segment would show a school an empty list and imply there is no fraud, which is worse than showing the unfiltered list. Attribute the alerts first, then segment them.