Implement a huh-native MultiSelectWithSearch that renders the search
input and multi-select list simultaneously using LayoutStack. The
search input is in Group 0 and the multi-select in Group 1, with
OptionsFunc bound to the search query so results update when the
user presses Enter to advance focus. Users can Shift+Tab back to
refine their search, and selections persist across queries.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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