Layout::multiple(n) maps counts without a fixed grid to a near-square
grid (3 -> 2x2, 5 -> 3x2), but Layout::Multiple kept only the grid, so
layout() filled every cell: three per sheet put four pages on a sheet.
Layout::Multiple now carries per_sheet, capped by the grid; spare cells
stay blank and cut-stack piles use the same count. The doc_print tool
and the print dialog pass the count through.
Co-authored-by: Claude Opus 5.5 <[email protected]>
