CngxDataGridHeader

The column-header row of a CngxDataGridAccordion. Lays its projected cngxDgaCells out on the shared --cngx-dga-columns grid so the labels align with the data columns below. It is exposed to assistive tech (no aria-hidden) so a cngxDgaSortHeader cell is reachable: a focusable sort control inside an aria-hidden subtree would be pruned from the accessibility tree and fail aria-hidden-focus, and aria-hidden cannot be undone by a descendant. The plain label cells now read like a table header row - a small, acceptable trade for keeping the sort controls operable. Each data row still announces its own name through its primary cell, so the disclosure list stays legible.

It is also the single column source: the group reads these header cells and derives the shared grid-template-columns from each cell's col track intent (grow / fit / sm / md / lg), so the columns are defined where they are labelled rather than in a separate template string.