-spec channels() -> [#{channel_id := binary(), members := non_neg_integer()}].

Every chat channel running on this node, with its current member count.

Two ETS reads and one pg lookup per channel: no channel process is called, so an operator listing channels cannot block behind one that is busy.

The registry is the source rather than pg:which_groups/1, which the console this replaces used. pg drops a group when its last member leaves, so a running channel nobody is currently joined to is simply absent there - and the console asked the wrong scope besides, so its channel list was always empty.

Capped at 1000 channels, the same ceiling asobi_leaderboards:boards/0 enumerates under, so the in-memory sort behind this stays bounded. [] before the chat supervisor has started, and members => 0 for every channel when pg has not.