Each ProviderAccount can now have multiple base URLs (provider_urls table).
On stream failure, BroadcastGroup cycles to the next domain immediately
with no wait; backs off only after all domains have been tried once.
Background health checker pings every domain every 5 min via player_api.php
and updates status/response_ms. Admin UI shows domain list with color-coded
status badges and a "Verificar todos" button per provider.
joaquin
cccdf9f137