docs: replace 1.3.9 beta guide with 1.4.0 checklist Publish Beta-Test-Guide-v1.4.0 as the active prerelease checklist, supersede the v1.3.9 page with a short notice, and point Home/Sidebar at the new guide. Co-authored-by: Cursor <cursoragent@cursor.com>
Updated Beta Test Guide — v1.3.9 (markdown)