An omitted trusted_proxies key now defaults to 10.0.0.0/8, 172.16.0.0/12
and 192.168.0.0/16 instead of trusting no one, matching the deployment
where pixa sits behind a proxy on a private network. An explicitly empty
list still trusts nothing, and an explicit list replaces the default;
these are distinguished by parseCIDRList returning nil only for an absent
key. Loopback is excluded, as it is not an RFC 1918 range.
Model: opus-4-8