Release v1.4.0

Release bookkeeping only: VERSION to v1.4.0, the [Unreleased] heading dated as ## [1.4.0] -- 2026-08-25, and just sync propagating the version into the five .reference.yaml pins so newly stamped projects do not start a minor behind.

The release body was read before tagging rather than after, which is what caught the two over-long entries fixed in !88 (merged). just validate-release-notes now passes for v1.4.0 and all four refusals still refuse.

Contents: the details.idx-group scanning layer, two authoring rulings on /design/authoring/, the index-row type-size fix, and the release page carrying the version's CHANGELOG section. First release whose tag body is built from that section rather than typed at tag time.