Add home schedule view toggle

[ShankarK2009]

Summary

• add a persistent Full periods / Half periods selector to Home when the bell schedule provides A/B times
• expand personalized classes, lunch, advisory, and free time into accurate half-period cards and countdown states
• keep canonical notification timelines unchanged and hide the selector when half-period data is unavailable

Validation

• swift test --package-path Packages/ScheduleKit (181 tests passed)
• xcodebuild -quiet -project "Stevenson Space Companion App.xcodeproj" -scheme "Stevenson Space Companion App" -destination "generic/platform=iOS Simulator" -derivedDataPath /tmp/stevenson-schedule-mode-derived CODE_SIGNING_ALLOWED=NO build