Boost version to 1.21.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Anthony Green2026-04-01 23:26:50 -0400 505a4eb155e3afb3d62975143b949294ecfa00fb
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>