`span={{ md: 8 }}` now covers the full row below md and 8 columns from
md, like Bootstrap's `col-md-8`, instead of 1 column on phones. A span
given as a number, or no span, is unchanged, and `columns` and `offset`
keep their defaults (1 and 0) when a map has no `base`.

The From Bootstrap table now maps `.col-md-8` to `span={{ md: 8 }}`, and
the metadata, CHANGELOG and ROADMAP release steps say so. Tests cover the
calculation, the rendered CSS on web and the native styles.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Uzb6PkC3SSJgt6PZyKhdND