feat: add manual update check

[rrbe]

Summary

• add a manual update check row to Settings that calls the existing Sparkle check flow
• keep automatic update copy focused on background checks
• make local build.sh replace placeholder Info.plist versions with the latest git tag for local builds

Verification

• swift test
• ./build.sh
• confirmed dist/LocalShare.app and ShareExtension.appex report 0.10.0 (69) locally