The composer's render path already paginates with center-tracking, but the
source list was hard-capped at 6 entries — so pressing Down arrow past
index 5 had no entries to land on. Repro: with ~37 slash commands, hitting
Down repeatedly stuck at the last visible row.
Bumping the source cap to 128 lets the existing viewport scroll logic
exercise the full filtered command list. No render-path change needed.
Fixes#64
Hunter Bown
320325e419