Both POST /login (HTML form) and POST /api/v1/auth/login now flow through
the shared attemptLogin() handler. Locked accounts respond with 401 +
Retry-After (generic body "Invalid credentials" / "Invalid username or
password") so attackers can't use lockout state as a username-existence
oracle.
@fastify/rate-limit registered with global=false; only the two login
routes opt in via per-route rateLimit config. File uploads and downloads
keep full throughput. Custom errorResponseBuilder logs AUTH_RATE_LIMITED
fire-and-forget so fail2ban can pick it up.
createTestApp now accepts Partial<Config> overrides so integration tests
can dial thresholds down without env-var mutation.
