Aggregate the per-day workout logs into performance stats:
- WorkoutDayLog.volume + StatPeriod/WorkoutStat/StatBucket.
- WorkoutViewModel.stat/statInterval/statBuckets (current vs previous).
- WorkoutStatsView: Day/Week/Month selector, Workouts/Sets/Volume cards
with %-delta vs previous period, metric chooser, and a Swift Charts bar
trend. Reached via a chart button in the Workout header.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>