Both /queue and /quit registered 'q' as an alias. Since /quit appeared
later in COMMAND_REGISTRY, _build_command_lookup() silently overwrote
/queue's claim, making the documented /queue shorthand unusable.
Fix: remove 'q' from /quit's aliases. /quit already has 'exit' as an
alias plus the full '/quit' command. /queue has no other short alias.
Closes#10467