Summary

• replace the manual SwiftPM app bundle packaging path with an Xcode-based app build
• make DMG creation reuse the same app packaging script and pass version/build numbers into Xcode
• document the official Sparkle release flow for local apps, DMGs, and appcasts

Verification

• ./scripts/package-app.sh 0.2.0 2
• copied verified 0.2.0 build 2 app to ~/Downloads/SlamDih.app
• ./scripts/create-dmg.sh 0.2.1 3
• ./scripts/generate-appcast.sh .build/dmg
• mounted .build/dmg/SlamDih-0.2.1.dmg and verified app version/build plus codesign
• bash -n scripts/package-app.sh scripts/create-dmg.sh scripts/generate-appcast.sh
• swift test