Apply degradation preference to the backup codec sender
Degradation preference is a sender-level property, and a backup codec
publishes over its own sender. Only the primary sender was configured, so
the backup encoder resolved a preference implicitly from the browser and
could adapt along a different axis than the primary.
Apply the resolved preference when a simulcast (backup codec) sender is
registered, and keep every sender in sync when the preference changes
after publish.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
