The shipped default (bind 0.0.0.0 + no API-key requirement) is a deliberate,
documented local-first posture — but an operator on an untrusted network
should learn that at startup, not after a surprise quota bill. serve now
prints a loud warning naming both escape hatches (REQUIRE_API_KEY=true or
OMNIROUTE_SERVER_HOST=127.0.0.1) whenever the resolved bind is non-loopback
and no key is required. Silent on loopback binds and when REQUIRE_API_KEY is
enabled. The default posture itself is unchanged (operator decision).