Sends alerts to a configurable Ntfy topic on: new user registration,
account lockout after 5 failed login attempts, and login attempts on an
already-locked account. Fire-and-forget — never raises if Ntfy is down.
Configure via NTFY_URL and NTFY_TOKEN in .env.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
