Grouped rows and columns now get Excel's outline band beside the headers:
a bracket per group, a -/+ button on the summary line and level buttons
in the corner. The buttons run data.hideDetail / data.showDetail and the
new data.showLevels, so they undo. Hide Detail marks the summary line
collapsed, Show Detail keeps inner groups that were collapsed on their
own, and Group / Ungroup take by: rows|cols. Show Detail and Hide Detail
are on the Data tab and in the Data menu, the group shortcuts are listed
as Alt+Shift+Right / Left, and shortcut lookup reads navigation keys by
their logical key so the numpad arrows work.
Fixes#373
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
