Other-model downloads now default to a flat layout, so a fresh library shows an
empty folder tree there while the sidebar still consumes 230px. Default the
per-page visibility to hidden for "other" through a small per-page default set.
The preference stays persisted per page, so an explicit show/hide toggle wins
afterwards, and the existing edge indicator keeps the hidden sidebar
discoverable and recoverable. Primary pages keep their visible default.
Will Miao