[Server] listChanged is not announced for a registry wired to the bus by the caller #607

#593 was too strict, my bad: listChanged is only announced with the built-in registry now, since a registry passed via setRegistry() "can't be wired to the bus". But the caller can wire it - symfony/mcp-bundle does exactly that:

$bus = new InMemoryNotificationBus();
$registry = new Registry(new PublishingEventDispatcher($bus));

$server = Server::builder()
    ->setServerInfo('test', '1.0.0')
    ->setRegistry($registry)
    ->setNotificationBus($bus)
    ->build();

$registry->registerTool($tool, $handler);

The notifications/tools/list_changed reaches the bus, but toolsListChanged is false => server/discover drops listChanged, subscriptions/listen agrees to none of the list-change types, and bundle users lose list-change notifications on 2026-07-28 altogether.

Options I see:

a) announce listChanged for a registry from setRegistry() as long as a bus is set, and keep it off initialize as #593 does
b) let the caller say so explicitly, e.g. setRegistry($registry, publishesChanges: true)
c) the bundle calls setCapabilities() - works, but every bundle server gives up capability detection for it

I'd go with b), a) would bring back the false announcement from chr-hertel#76. WDYT @Nyholm @CodeWithKyrian?