Add Sparkle update support

[serkansepil]

Summary

• add Sparkle 2 updater integration and an Update button in the popover
• bundle and sign Sparkle.framework in the macOS app package
• publish a signed Sparkle appcast to GitHub Pages from the release workflow
• bump app version to 0.1.2 / build 3

Verification

• swift test
• bash -n build.sh
• bash -n package-dmg.sh
• plutil -lint Info.plist
• git diff --check
• local app bundle codesign verification