chore(router): address the hosted router by hostname, TLS verification on

router.allaigate.com now resolves and serves a valid certificate, so the
hosted routing API no longer has to be reached by bare IP with certificate
verification switched off. Make https://router.allaigate.com the default
[router].url with verify_tls = true.

Existing configs still pointing at 138.226.222.209 (with or without a scheme
or a trailing slash) are moved to the hostname on load and have verification
restored, then saved: it is the same machine, and this is the difference
between a verified connection and a blind one. A self-hosted router URL is
left untouched.

README, docs/ROUTER.md (both languages), config/gateway.example.toml and
bench/accuracy.py follow.

Verified live: the migration rewrites a legacy config on startup, admin
health reports the hostname reachable over verified TLS (389 ms), and real
requests route through it - "math"/medium 0.416 and "translation"/low 0.268
with route_source=router.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cortiq-gateway"
-version = "0.2.46"
+version = "0.2.47"
 edition = "2021"
 rust-version = "1.75"
 license = "Apache-2.0"