A new 'Workouts Mac' target (same bundle ID as iOS, universal purchase)
with a NavigationSplitView shell over the shared data/sync layers:
routine management with starter gallery and seed-fork follow, schedule
editing (reminders stay iPhone-scheduled), and a browse-only exercise
library with the animated figures and reference guides.
Multi-writer stance: the Mac writes only routine and schedule documents
(whole-document last-writer-wins) and never workout documents, whose
per-log merge exists only on the watch ingest path. The Mac reconciles
on window activation (throttled) since iCloud syncs while the app is
closed, and flushes pending writes on deactivation.