I'm not seeing any way to manage playlists at all - I've dug through every interface and can't find a darned thing, or some problem in my configuration may be preventing it from appearing.  If this is covered in the documentation for 3.0, I can't find it.  Can anyone point me in the right direction?

I think you just need to enable auto dj -- in your config settings under the auto dj tab -- once you enable it the playlist manager and media library links should appear

I don't seem to HAVE an AutoDJ tab under my config settings.  (??)

When you set the account up, what did you choose? It would depend on what the server admin has installed, for  example, Shoutcastv2 and sc_trans (auto dj) --- or ShoutcastV1 and icess_cc (auto dj)

Figured out that - I hadn't set up my streaming engines properly.

But now, when I try to set up a user, I get this:

Unhandled exception: Cluster host authentication failure for Local server: authentication failed in /usr/local/centovacast/system/class_RPCDaemonClient.php:897

#0 /usr/local/centovacast/system/class_RPCDaemonClient.php(897): RPCDaemonClient::send()
#1 /usr/local/centovacast/system/class_RPCDaemonClient.php(849): RPCDaemonClient->send()
#2 /usr/local/centovacast/system/class_RPCDaemonClient.php(750): RPCDaemonClient->command()
#3 /usr/local/centovacast/system/class_GenericDaemonClient.php(127): RPCDaemonClient->remove_quota()
#4 /usr/local/centovacast/system/class_SystemControl.php(977): GenericDaemonClient::factory()
#5 /usr/local/centovacast/system/class_SystemControl.php(313): SystemControl->api_provision()
#6 /usr/local/centovacast/web/class_AccountEditor.php(875): SystemControl->__call('provision', Array)
#7 /usr/local/centovacast/web/class_AccountEditor.php(265): AccountEditor->provision_account()
#8 /usr/local/centovacast/web/reseller/modules/class_Module_accounts_base.php(65): AccountEditor->create()
#9 /usr/local/centovacast/web/admin/modules/class_Module_accounts.php(47): Module_accounts_base->create_account()
#10 /usr/local/centovacast/web/class_WebApplication.php(215): Module_accounts->execute()
#11 /usr/local/centovacast/web/admin/class_AdminApplication.php(64): WebApplication->execute()
#12 /usr/local/centovacast/web/admin/index.php(49): AdminApplication->execute()
#13 {main}

Which apparently means it thinks it's supposed to be a cluster host, and for some reason that's not a fine thing with it at the moment.

So, back to square one.