Resolves plan item A.1 (option б): login/setup rate-limiting used
RemoteAddr only, which behind the default reverse proxy is the proxy's own
address, making the limiter effectively global and enabling a lockout-DoS.
Now, when the request's direct peer matches the new TRUSTED_PROXY_CIDR list
(comma-separated CIDRs, env, empty by default), the last X-Forwarded-For
entry is used instead, giving a real per-client limit. Unset behaviour is
unchanged.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>