iframe=true now hides the sys bar for all users (previously trusted_access
users still saw it). Admins can pass show_menu=true to re-enable it while
testing an embedded page like video_conferences.
hide_menu=true remains for non-iframe hide use cases (kiosk, etc).
Updated URL builder: hide_menu checkbox → show_menu checkbox.
Updated GUIDE__Development.md URL params table.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>