Single attemptLogin() orchestrates lockout check, bcrypt verify (against
real or dummy hash), success/failure logging, and a configurable minimum
response-time clamp. Both login routes will share this — no duplication.
Adds three logger events for the operator's escalation pipeline:
AUTH_LOCKOUT_TRIGGERED, AUTH_LOCKED_ATTEMPT, and AUTH_RATE_LIMITED.
fail2ban filters can pick these up to escalate persistent attackers from
in-app lockout to IP ban.
Constant-time defense: unknown users still pay bcrypt cost (via dummy hash)
and the clamp ensures locked-vs-unknown-vs-wrong-password aren't
distinguishable by response time. Username is canonicalized (lowercase + trim)
before lookup so attackers can't bypass lockout via case variation.
