Expanded `!` bash and `eval` execution output kept rendering the
`… N more lines (ctrl+o to expand)` footer after Ctrl+O revealed every
line, because `hiddenLineCount` was computed from the collapsed preview
window regardless of the `#expanded` (or sixel-passthrough) state.
Zero the hidden count whenever the full output is shown so
`buildStatusFooter()` stops advertising hidden lines and ctrl+o.
Fixes#5842
roboomp
ea78e346d0