Review follow-up: the explicit model.provider: openrouter pin is provider
intent regardless of the base_url host, because the runtime treats a
non-openrouter base_url under the openrouter pin as a deliberate
mirror/proxy (runtime_provider_backends.py #10622, pinned by
test_explicit_openrouter_honors_config_base_url_mirror). Preserve that
intent instead of rejecting the mirror and parking the dashboard on
Setup Required.
Also correct the stale-base_url regression example: a non-loopback
base_url under a bare (unpinned) provider is the '#14676 stale leftover'
case; an openrouter pin is the one provider where a foreign host is a
legitimate mirror, not staleness.
Add the mirror URL to the bootstrap regression coverage and map the
contributor email for the attribution gate.
Refs #109397
(cherry picked from commit f59e511118861c168da7d5c64f4b5c8640de8b61)
