HeaderCell now accepts `compactWidth` alongside `width`. `width` applies
at default (wide) viewports; `compactWidth` overrides in the compact
container-query band (≤720px). Both fall back to `minmax(0, 1fr)` —
existing callers stay unchanged.

This unlocks the BI/data-reporting layout: evenly-distributed columns
on desktop (visual balance) and content-aware columns at narrow widths
(badge column shrinks to max-content, the action column absorbs the
slack so its hint text fits without ellipsis truncation).

Implementation: extractColumnMeta now returns both `template` and
`compactTemplate`, and gridColumnsResponsive() accepts both, emitting a
single StyleX style with three tiers (default / compact / stack) — all
gridTemplateColumns rules live in one class so StyleX's
last-style-wins conflict resolution can't drop any of them.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>