why: release the JS toolchain major upgrades (Zod 4, Vitest 4,
TypeScript 6, Tailwind CSS 4.3, Vite 8) and the theme assets'
Baseline Widely Available browser floor.

what:
- Bump all workspace packages 0.0.1a27 → 0.0.1a28
- Date CHANGES entry for 0.0.1a28 (2026-06-07)
- Add 0.0.1a29 unreleased header