Earlier in the PR the new configs (linkedin.oauth_api, youtube.oauth_api,
bluesky.default_service, mastodon.default_instance) were only read by
ConnectionVerifier. The same URLs were still hardcoded in the publishers,
analytics and the Bluesky auth controller — meaning a self-hosted user
setting BLUESKY_DEFAULT_SERVICE or MASTODON_DEFAULT_INSTANCE in env would
get split behavior: refresh/verify honor the override, publish/analytics
don't.
Routes all 10 remaining call sites through the same config values so the
overrides actually work end-to-end.
