0.5.2-beta.3

ci(demo): add notarize input to demo prerelease workflow (#20)

Lets a demo prerelease be cut signed-only (notarize=false) while the Apple
notarization agreement is pending, instead of failing the whole run. Defaults
to true. Signed-only builds open with xattr -dr com.apple.quarantine.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>