_client_ip trusted the first X-Forwarded-For hop unconditionally, so anyone able to
reach the app port could forge XFF and dodge the login/register/reset/demo rate limits.
Now trust XFF ONLY when the request's socket peer is a configured reverse proxy
(settings.trusted_proxy_ips, e.g. the VPS Caddy's WireGuard peer IP), and take the
RIGHTMOST entry — the client our proxy actually saw and appended, immune to a client
pre-seeding a fake XFF. A request from any other peer (hitting the port directly) is
keyed on its real socket IP, so XFF can't be forged to bypass the limits.
New TRUSTED_PROXY_IPS env (empty default = no proxy, use the direct peer). Documented in
.env.example, docs/self-hosting.md, README. Unit-verified against spoof-through-proxy and
direct-bypass cases.
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